Abstract:
Sport ball training devices and methods for releasably holding a tennis ball or other sport ball at an appropriate height for the practice of striking the ball, either directly or indirectly with a racket or the like. An embodiment may have a support device with a base and an adjustable vertical tubular assembly for the support of a transverse arm from which a ball sling is suspended. A retainer member of the ball sling circumferentially holds a sport ball. An embodiment of the retainer member may be made from an elastometric material that lightly squeezes the ball with sufficient force to restrain it, but releases easily when the ball is hit so that the trajectory of the ball is not affected by the presence of the retainer member nor is the racquet significantly affected by the presence of the ball sling generally.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims priority under 35 U.S.C. section 119(e) from U.S. Provisional Patent Application Ser. No. 60/489,959, titled “SPORT BALL TRAINING DEVICE AND METHOD”, filed Jul. 23, 2003, by John L. Wardle and James M. Jensen and U.S. Provisional Patent Application Ser. No. 60/517,935, titled “SPORT BALL TRAINING DEVICE AND METHOD”, filed Nov. 5, 2003, by John L. Wardle and James M. Jensen, both of which are also incorporated by reference herein in their entirety. 
     
    
     BACKGROUND  
       [0002]     Many sports require the hitting of a ball using different techniques to gain a competitive advantage in a game. For example in the sport of tennis the technique of making the ball spin as it travels through the air provides some distinct advantages. One ground stoke technique is that of hitting a ball with top spin in which the ball can driven through the air at a high velocity and still remain in play due to the curved flight path that the ball takes. This technique requires a specific stoke pattern to be developed which is difficult to master when a balls are delivered by a ball machine or an assistant because the balls are in constant motion and they typically land in different positions with varying characteristics of bounce. When a mistake is made by a player or student attempting to learn a particular stroke technique, it can be difficult for the player to analyze and correct the problem due to the many inherent variables. Some of the existing devices for tennis training allow a player to practice repeated hits from a fixed location, however, these devices are often difficult to use or transport. In addition, for the existing training devices, the ball is typically fixed to some sort of tether or requires special modification of a ball in order to release from the device, which may have an adverse effect on the flight path and give the player a distorted perception of the success of their attempt to hit the ball. What has been needed are training techniques and devices to support the techniques that are simple and easy to implement, can accommodate any type of ball typically used in the game, including well worn practice balls, and that yield a natural and realistic flight path for a ball hit using the techniques and devices.  
       SUMMARY  
       [0003]     In one embodiment, a sport ball training device includes a support device and a ball sling with at least one resilient sling member which has a first end secured to the support device. The resilient sling member is configured to elastically assume a predetermined configuration when in a relaxed state. A retainer member is secured to a second end of the resilient sling member and has a loop which is configured to releasably secure a sport ball.  
         [0004]     In another embodiment, a sport ball training device includes a support device and a ball sling having a first resilient sling member with an upper end secured to the support device. The ball sling also has a second resilient sling member with an upper end secured to the support device. A retainer member is secured to lower ends of the resilient sling members and includes a loop configured to releasably hold a desired sport ball.  
         [0005]     These and other advantages of embodiments will become more apparent from the following detailed description when taken in conjunction with the accompanying exemplary drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]      FIG. 1  is a perspective view of an embodiment of a sport ball training device.  
         [0007]      FIG. 2  is a detail view broken away of a transverse support arm of the sport ball training device of  FIG. 1 .  
         [0008]      FIG. 2A  is an elevational view of a ball sling of the sport ball training device of  FIG. 1 .  
         [0009]      FIGS. 2B-2D  are transverse cross sectional views of the ball sling of the sport ball training device of  FIG. 2A  taken along lines  2 B- 2 B,  2 C- 2 C and  2 D- 2 D, respectively.  
         [0010]      FIG. 3  is an enlarged view of a connection between an upper end of a resilient sling member and the transverse support arm of the sport ball training device of  FIG. 1  indicated by the encircled portion  3  of  FIG. 2 .  
         [0011]      FIG. 4  is an enlarged view broken away of the retainer member of  FIG. 2  including a loop configured to releasably secure a sport ball which is shown disposed within the loop.  
         [0012]      FIG. 5  is a perspective view of an embodiment of a ball sling having two resilient sling members secured between support device connectors in the form of rings at the upper ends of the sling members and a retainer member in the form of a resilient loop at the lower ends of the sling members.  
         [0013]      FIG. 6  is a perspective view of another embodiment of the ball sling having a single resilient sling member secured to a support device connector at the upper end of the sling member and a retainer member in the form of a resilient loop secured to a lower end of the sling member.  
         [0014]      FIG. 7  is a front view of another embodiment of a ball sling.  
         [0015]      FIG. 7A  is a side view of the ball sling of  FIG. 7 .  
         [0016]      FIG. 8  is a view in partial section of the ball sling of  FIG. 7 .  
         [0017]      FIG. 9  is an enlarged view in partial section of the ball sling as indicated by the encircled portion  9  of  FIG. 8 .  
         [0018]      FIG. 10  is an enlarged view in partial section of a sling member as indicated by the encircled portion  10  of  FIG. 8 .  
         [0019]      FIG. 11  is an enlarged view in partial section of the ball sling as indicated by the encircled portion  11  of  FIG. 8 .  
         [0020]      FIG. 12  illustrates another embodiment of a ball sling.  
         [0021]      FIG. 13  is an enlarged view of the ball sling as indicated by the encircled portion  13  of  FIG. 12 .  
         [0022]      FIG. 14  illustrates another embodiment of a ball sling.  
         [0023]      FIG. 15  is an enlarged view of the ball restraining sling as indicated by the encircled portion  15  of  FIG. 14 .  
         [0024]      FIG. 16  is an exploded perspective view of the sport ball training device of  FIG. 1  showing various components of the embodiment.  
         [0025]      FIG. 17  is a perspective view of an embodiment of a support device base knuckle from the base of the device of  FIG. 16 .  
         [0026]      FIG. 18  is a perspective view of an embodiment of a support device horizontal knuckle clamp from the upper end of the vertical tubular assembly of  FIG. 16 .  
         [0027]      FIG. 19  is a perspective view of an embodiment of a split collet for the tubular riser assembly of the support device in  FIG. 16 .  
         [0028]      FIG. 20  is a perspective view of an embodiment of a sport ball training device illustrating an optional extension arrangement for the tubular riser assembly of the sport ball training device of  FIG. 16 .  
         [0029]      FIG. 21  is an enlarged view of the tubular riser assembly of the sport ball training device of  FIG. 20  indicated by the encircled portion  21  in  FIG. 20 .  
         [0030]      FIG. 22  is a side view of the sport ball training device of  FIG. 1  set up for hitting a ball with topspin with a sport ball disposed within the loop of the ball sling.  
         [0031]      FIG. 23  is a side view of the sport ball training device of  FIG. 22  after the ball has been hit with a topspin inducing stroke of the racquet.  
         [0032]      FIG. 24  is a perspective view of the sport ball training device of  FIG. 23  with the ball sling winding around a horizontal support arm due to recoil from the racquet impact during the stroke.  
         [0033]      FIG. 25  is a side view of the ball sling of the sport ball training device of  FIG. 1  with the sport ball disposed within the ball sling of a sport ball training device after impact from a racquet and indicating by the various arrows the forces and movements of the sport ball and ball sling.  
         [0034]      FIG. 26  is a perspective view of the ball sling and sport ball of  FIG. 25 .  
         [0035]      FIG. 27  is a perspective view of an embodiment of the sport ball training device of  FIG. 1  partially collapsed for transportation.  
         [0036]      FIG. 28  is a perspective view of the sport ball training device of  FIG. 27  fully collapsed for transportation. 
     
    
     DETAILED DESCRIPTION  
       [0037]     Various embodiments of the invention are directed to methods and devices for assisting a player training in sports involving hitting a sport ball with a racquet, bat or other device. In one embodiment a device for the development of various tennis stokes is described where the device will not offer significant resistance to or deflection of the racket when the ball is struck, nor will the embodiment cause interference with the follow through of the racquet. Embodiments may be configured to hold a sport ball at a pre-determined height and allow the ball to travel freely and naturally when hit by a racquet without any detrimental initial restraining force exerted by the device on the ball at the time of impact. An embodiment includes a lightweight sport ball training device that can be folded quickly and easily into a compact size for transportation. Embodiments of the device include a resilient ball sling that will unwrap or uncoil itself from a transverse support arm after a ball disposed within a retainer member of the ball sling has been struck with a racquet, bat or similar device which also imparts motion to the sling. Embodiments of the ball sling which automatically uncoil or unwrap from a support arm or other supporting portion of the support device may include a resilient sling member or portion that has elastic, spring-like or superelastic properties. Embodiments of the ball sling can include a modular configuration that is designed such that the ball sling, or portions thereof, can be easily replaced when worn or damaged.  
         [0038]     An embodiment of a sport ball training device  10  configured for use with a tennis ball  12  includes a ball sling  14  that hangs from a transverse support arm  16  of a support device  18  as shown in  FIG. 1 . The ball sling  14  is used to hold the ball  12  stationary at a pre-determined height for contact with an instrument such as racquet  19 . The ball sling  14  is configured with a retainer member  20  that includes a loop  22  that is used to hold the tennis ball  12  in a stationary position and is more clearly shown in  FIG. 2 .  
         [0039]     The embodiment of the loop  22  shown in  FIGS. 1-4  may be constructed from of an elastic or elastomeric material and has an inner circumference that may be chosen as a particular function of the nominal outer diameter of the ball it is intended to restrain, depending of the qualities of the specific ball. For example, the inner circumference of the loop  22  may be the same as or slightly larger than the outer circumference of a light weight textured ball, such as a tennis ball. The texturing or “fuzziness” of a tennis ball may facilitate retention within the loop  22  and allow a loose fit. On the other hand, heavy smooth surfaced balls, such as baseballs, may require a loop  22  that has a nominal inner circumference that is slightly smaller than the outer circumference of the ball, that the loop  22  is configured to hold. Embodiments of the loop  22  may restrain the ball by surface friction between the ball  12  and the loop  22 , compressive force between the ball  12  and the loop  22  or both. Compressive force is generally applied to an outer surface  23  of the ball  12  along a plane that intersects or nearly intersects the center of the ball  12 . With regard to embodiments using heavy smooth surfaced balls, such as baseballs, the retainer member  20  can restrain the ball  12  by compressive force. Balls that have surface texture e.g. tennis balls having a fuzzy or fibrous type outer surface may only require close contact between the outer surface  23  of the ball  12  and the loop  22  to be restrained as the fibrous surface grips the sling by surface friction with sufficient force to maintain the position of the ball  12  in the loop  22 .  
         [0040]     In one embodiment, the loop  22  is made from an elastic material that is sufficiently resilient for the loop to maintain a substantially round open configuration in a relaxed state to facilitate placement of a sport ball within the loop. Embodiments of the loop  22  may have an inner circumference of about 5 percent smaller to about 5 percent larger than an outer circumference of a sport ball  12  for use with the training device. In another embodiment, an inner circumference of the loop  22  is about 3 percent to about 7 percent smaller than an outer circumference of a sport ball  12  for use with the training device. In another embodiment, an inner circumference of the loop  22  is about 3 percent to about 7 percent larger than an outer circumference of a sport ball  12  for use with the training device. In yet another embodiment, the loop  22  has an inner circumference of about 8.0 inches to about 9.0 inches. An embodiment of the elongate looped element  21  of the loop  22  that forms the loop  22  can have an outer transverse dimension or diameter of about 0.12 inches to about 0.16 inches.  
         [0041]     The ball sling  14  also includes a first sling member  24  and a second sling member  26 . The first sling member  24  has an upper end  28 , a lower end  30  and a shock absorbing zone  32 . The upper end  28  has a cavity  34  with a recessed portion  36  configured to elastically capture an enlarged portion  38  of a barb  40  that is secured to and extends downward from the transverse support arm  16  of the support device  18  as shown in  FIG. 3 . This configuration allows the upper end  28  of the first sling member  24  to be easily installed and removed from the transverse support arm  16  for transport or replacement. The second sling member  26  may have the same or similar features, dimensions and materials as those of the first resilient sling member  24 . The second sling member  26  has an upper end  42 , a lower end  44  and a shock absorbing zone  46 . The upper end  42  of the second resilient sling member  26  may be secured to the transverse support member  16  in the same fashion as the first resilient sling member  24 . Another barb  47  is provided on the transverse support arm  16  for the upper end  42  of the second sling member  26 .  
         [0042]     The upper ends  28  and  42  of the first and second resilient sling members  24  and  26  may be separated by a greater distance than the distance between the lower ends  30  and  44 , which may be joined together in some embodiment, such as the embodiment of  FIGS. 1-4 . As such, the resilient sling members  24  and  26  form an angle indicated by arrow  48  between them. The angle indicated by arrow  48  may be from about 10 degrees to about 60 degrees for some embodiments, more specifically, about 15 degrees to about 25 degrees. This triangular arrangement between the transverse support arm and the retainer member  20  give the ball sling  14  a stable configuration that minimizes the amount of undesired side to side movement of the ball  12  while disposed within the ball sling  14 . In addition, this arrangement helps to minimize rotation of the ball sling  14  and maintain the ball sling  14  in a single plane while in the resting position with the exposed surface of the ball facing rearward for impact by a racquet or the like without hitting the loop  22 .  
         [0043]     The sling members  24  and  26  have a tapered configuration wherein the outer transverse dimension or diameter of the sling members  24  and  26  tapers to an increased dimension from the lower ends  30  and  44  to the upper ends  28  and  42 . For embodiments of the sling members made from a uniform material, such as an elastic polymer, this creates an increase in resistance to bending from the lower ends  30  and  44  to the upper ends  28  and  42  for each of the resilient sling members  24  and  26 . This configuration provides a resilient propensity to recoil and assume the substantially straight configuration of the resting position of the resilient members  24  and  26  after being struck by a racquet or the like. In one embodiment, the resilient sling members  24  and  26  may have an inclusive taper angle of about 0.5 degrees to about 5 degrees, more specifically, about 0.5 degrees to about 1.0 degrees. In another embodiment, the resilient sling members  24  and  26  may have an inclusive taper angle of about 0.5 degrees to about 1.5 degrees. Embodiments of the sling members  24  and  26  may have a length of about 12 inches to about 25 inches for some embodiments.  
         [0044]     The entire ball sling  14  may be made from a monolithic structure of elastic or elastomeric material capable of absorbing shock during impact of a racquet on the ball  12 . However, the majority of shock absorption after impact on the ball  12  occurs in the shock absorbing zones  32  and  46  located on the sling members  24  and  26  adjacent the retainer member  20  and in the loop  22  of the retainer member  20 . For the configuration of the embodiments of sling members  24  and  26  the majority of the shock absorption within the sling members  24  and  26  occurs within the zones  32  and  46  because of the tapered configuration of the sling members  24  and  26  produces a smaller transverse dimension or diameter in the lower portions of the sling members  24  and  26  which thereby results in lower resistance to stretching in the zones  32  and  46 . The loop  22  of the retainer member  20  absorbs a high percentage of shock on impact for the same reason, specifically, the transverse cross section and corresponding resistance to stretching of the loop  22  is similar to that of the shock absorbing zones  32  and  46 . In other embodiments discussed below, alternate structures for the purpose of shock absorption zones adjacent the retainer member  20  are discussed.  
         [0045]     Embodiments of the loop  22  of the retainer member  20 , as well as the ball sling  14  generally, may be made from any suitable elastic, resilient material. It may also be useful for the material of the ball sling  14  including the loop  22  to be resistant to breakage and fatigue as repeated impact from a racquet or bat can be destructive. Materials such as silicones, polyurethanes, rubbers, mixtures or alloys of these, or the like may be used. In some embodiments, elastomers, such as thermoplastic elastomers, having durometers of 25 A shore to about 65 A shore may be used. Specific materials, such as Kraton® materials Dynaflex® G2711 and Dynaflex™ G2706, manufactured by GLS Corporation, in McHenry Ill., may be useful individually or in combination. Mixtures such as 50% Dynaflex G2706 and 50% Dynaflex G2711 and other mixtures such as 66% Dynaflex G2711 and 34% Dynaflex G2706 may be useful for construction of the ball sling  14  in general. The embodiment of the ball sling  14  shown in  FIGS. 1-4  may be a monolithic structure injection molded at one time from a substantially uniform material, such as the polymers discussed above. Such a method of manufacture reduces cost and manufacturing time and for some materials produces a strong and resilient ball sling  14 . A modification of the monolithic structure could also include methods of over molding one material over another to achieve the desired properties of multiple materials.  
         [0046]     For the embodiment of  FIGS. 1-4 , loading a ball  12  into the loop  22  of the retainer member  20  is achieved by simply stretching the loop  22  onto the centerline of the ball  12 . The loop  22  is configured such that the restraining force is enough to stop the ball  12  from falling out of the loop  22  on its own or by force of the ball&#39;s own weight, but not enough to restrain the ball  12  if it is lightly struck by a racquet, club, player&#39;s hand or other such device. Although the embodiment of the ball restraining device  10  shown in  FIG. 1  includes a loop  22  to restrain the ball  12 , other configurations are also contemplated. For example, a resilient fork or prong that encompasses a portion of a ball&#39;s outer surface and releasably restrains the ball may be used as a retention member  20  on the ball sling  14 . Also, a retention member  20  may use a loop with circumferentially spaced contacts points or ribs as is shown in  FIG. 15 .  
         [0047]     Referring to  FIG. 1 , the support device  18  includes a base  50 , a riser tube assembly  52  having a lower end  54  secured to the base  50 , and the transverse support arm  16  secured to and extending radially from an upper end  56  of the riser assembly. In the embodiment of  FIG. 1 , the transverse support arm  16  is substantially perpendicular to the riser tube assembly  52  in a horizontal position, but could also be set at another angle with respect to the riser tube assembly  52 . The base  50  includes a knuckle  58  pivotally secured to first ends  60 ,  62  and  64  of three legs  66 ,  68  and  70 , respectively, by clevis pins  71 . The legs  66 ,  68  and  70  extend radially and somewhat downward from the knuckle  58  when in a deployed state to form a stable three point contact base. The riser tube assembly may have at least two tubular members  72  and  74  with the first tubular member  72  configured to slide within the second tubular member  74  in a telescoping arrangement. A locking member  76  in the form of a split collet assembly with a threaded rotating locking ring  77  is disposed on an upper end  78  of the second tubular member  74  to prevent relative axial movement between the two tubular members  72  and  74  when in a locked position. The transverse support arm  16  is connected to a horizontal clamp or knuckle  80  with a clevis pin  82 . Horizontal clamp  80  in turn is permanently attached to the upper end  56  of the first vertical support tube  72 .  
         [0048]      FIGS. 5 and 6  show ball sling embodiments constructed from a single or uniform material. One method of manufacture for these and other ball sling embodiments would be injection molding of any of the materials discussed above with respect to the ball sling embodiment  14  of  FIG. 1 . The sling members may transition in transverse cross section from a first cross sectional area at the loop to a second greater transverse cross sectional area at the upper end of the sling member adjacent the support device. Such a transition in cross section of the sling members can provide ball sling recoil means to unwind the ball sling that wraps itself around the transverse support arm  16  after a ball has been hit. The ball sling embodiment  90  shown in  FIG. 5  has an alternate method of attachment to the transverse support arm  16 . Ball sling  90  has a pair of retention loops  92  and  94  secured to upper ends of sling members  95  and  97  which have a nominal inside diameter that is smaller than an outside diameter of the transverse support arm  16 . The retention loops  92  and  94  are stretched in order to place them over the transverse support arm  16  and are held in place by friction. This allows for easy replacement of the ball sling  90  if worn or damaged. The lower ends of the sling members  95  and  97  are secured to loop  99 . Other suitable means for providing easy replacement or modularity of the sling  90  can be used. Alternatively the ball sling  90  can be permanently attached to the transverse support arm  16 .  
         [0049]      FIG. 6  shows a ball sling embodiment where the ball sling  96  is constructed with a single sling member  98  that is in the form of a thin sheet of elastomeric material with a single retention loop  100  at the upper end  102  for attachment to a transverse support arm  16 . A lower end  104  of the sling member  98  is secured to a retainer member  106  having a loop  108  similar to the loop  22  of the ball sling  14  discussed above. The sling member  98  has a substantially constant thickness, but varies in width from a starting width at the lower end  104  adjacent the loop  108 , and tapering to a greater width at the upper end  102  adjacent the retention loop  100 . This configuration produces a sling member  98  having an increased resistance to longitudinal bending from the lower end  104  to the upper end  102  which facilitates recoil or unwinding of the ball sling  96  from a support member  16  after impact and subsequent winding about the support member  16 .  
         [0050]      FIGS. 7 through 11  show a ball sling  110  that is made from tubular elastomeric sling members  112  and  114  with free-floating resilient recoil wires  116  and  118  disposed within the sling members  112  and  114 . The recoil wires  116  and  118  may be made from a resilient spring material such as music wire, superelastic materials such as nickel titanium wire, fiberglass elements, or the like. The recoil wires  116  and  118  are secured to an upper portion of the resilient sling members  112  and  114  but free floating through an inner lumen of the lower portion of the sling members. This configuration leaves the lower ends of the sling members  112  and  114  unrestrained axially and free to stretch and absorb shock during impact. The recoil wires  116  and  118  also have an outer protective lubricious sheath  119  of resilient tubing such as Teflon® (PTFE), kynar or polyolefin placed over it which extends beyond the lower ends of the recoil wires  116  and  118  to serve as a strain relief.  
         [0051]     The strain relief protects the tubular elastomeric material of the sling members  112  and  114  and prevents the metal wire from puncturing through the sling member tube when the ball sling  110  is tightly flexed. This embodiment  110  also has a sleeve  126 , which is disposed tightly over the sling members  112  and  114  adjacent the retainer member  128 . Sleeve  126  can be bonded in place or left unattached so the user can adjust the circumference of the loop  130  of the retainer member  128 . The sleeve&#39;s  126  position is adjusted by stretching the ball sling  110 , which reduces the diameter of the components and allows the sleeve  126  to be repositioned. In other embodiments, the ball sling  110  may be made from an elongate elastomeric member having a reinforcement layer, such as a braid, disposed over the elastomeric tubing. The upper ends of the sling members  112  and  114  may be secured to the support  16  by a barb  132  in a fashion similar to that discussed above and shown in  FIG. 9 .  
         [0052]      FIGS. 12 &amp; 13  show another ball sling embodiment  140  that has sling members  142  and  144  constructed from metal spring wire. The lower portion or loop  146  of the sling members  142  and  144  are insert molded into an elastomeric loop  148  as shown by the dashed portion of the member in  FIGS. 12 and 13 . The spring metal sling members  142  and  144  of this embodiment are not coated or surrounded by any polymer or elastomeric material which provides a simple design that is suited mainly for low velocity impacts as it has no shock absorbing features other than the loop portion  148 . The metal spring sling members  142  and  144  may be made of any suitable metal, including spring steel and superelastic alloys, such as nickel titanium alloys.  
         [0053]      FIGS. 14 and 15  show another ball sling embodiment  150 . The spring metal sling members  152  and  154  of this embodiment are not coated or surrounded by any polymer or elastomeric material but shock absorbing sections  156  and  158  are incorporated in the sling members  152  and  154  in the form of a helical wind which reacts like an extension spring when exposed to tensile load. Striking balls at a high velocity may put high levels of stress on the ball sling  150 . These embodiments, as well as others, may employ shock absorbing features to overcome this problem. This embodiment also has a rigid retainer member  160  with a loop  162  made from high impact plastic e.g. polycarbonate nylon molded over the spring metal sling members  152  and  154 . Two or more inward radial protrusions  164  are attached to the rigid retainer member and are sized to make contact with and restrain a sport ball.  
         [0054]      FIGS. 16-19  illustrate the support device  18  of the sport ball training device  10  in an exploded view illustrating the cooperation of the various components of the embodiment. The support device  18  includes a base  50 , a riser tube assembly  52  having a lower end  54  secured to the base  50 , and the transverse support arm  16  secured to and extending radially from an upper end  56  of the riser assembly. The base  50  includes a knuckle  58  pivotally secured to first ends  60 ,  62  and  64  of three legs  66 ,  68  and  70 , respectively, by clevis pins  71 . The legs  66 ,  68  and  70  extend radially and somewhat downward from the knuckle  58  when in a deployed state to form a stable three point contact base. The riser tube assembly may have at least two tubular members  72  and  74  with the first tubular member  72  configured to slide within the second tubular member  74  in a telescoping arrangement. A locking member  76  includes a split collet  79  with a threaded rotating locking ring  77  threaded onto a threaded upper end  78  of the second tubular member  74 .  
         [0055]     The threaded lock ring  77  threads onto a threaded portion  78  of the upper end of the lower tubular member  74  with the split collet  79  disposed within the threaded cap and the upper tubular member  72  slidingly disposed within the split collet  79 , the threaded locking ring  77  and the lower tubular member  74 . Tightening of the threaded locking ring  77  forces the split collet  79  closed which then applies a restrictive compressive force on the upper tubular member  72  and fixes the upper tubular member  72  in relation to the lower tubular member  74 . The locked arrangement is reversed by unscrewing the threaded locking ring  77  so that the split collet  79  can return to its resting configuration which again allows the upper tubular member  72  to slide within it. The transverse support arm  16  is connected to a horizontal clamp or knuckle  80  with a clevis pin  82 . Horizontal clamp  80  in turn is permanently attached to the upper end  56  of the first vertical support tube  72 .  
         [0056]      FIGS. 20 and 21  illustrate another embodiment of the support device  170  which includes extension members  172  in order to achieve a desired amount of vertical adjustment.  FIGS. 20 and 21  show an embodiment of a support device  170  wherein the adjustable height can be increased by adding extension tubes  172  which dock together in a telescoping arrangement and are locked together by placing a retaining pin  174  or the like through the respective retainer pin holes  176  when they are aligned. The extension tubes  172  may have a male end  178  having a reduced outer diameter or transverse dimension which is configured to fit within a mating female end  180  having an inner transverse dimension or diameter that accepts the male end as shown in  FIG. 21 . With this configuration, multiple extension tubes may be used in series.  
         [0057]     The extension tubes  170  may be made to increase the height by increments of the working range of vertical adjustment of the tubular elements  72  and  74  of the riser tube assembly  52  shown in  FIG. 1 . The working range of the riser tube assembly  52  may be from about 15 inches to about 25 inches for some embodiments. Multiple extension tubes  172  can also be stacked onto one another in series to achieve any desired height which may be useful for some applications of the sport ball training device  10 . For example, an embodiment of a sport ball training device  10  that has a working height range for the ball  12  above the ground of about 20 inches to about 40 inches from the ground, may be useful for training in certain types of ground strokes in the game of tennis. The addition of one extension tube  172  of about 20 inches in length will increase the working height range to about 40 inches to about 60 inches. The addition of two extension tubes  172  in series will yield a working height range of about 60 inches to about 80 inches. The additional working height range may make the sport ball training device suitable for use with the training of volley shots and service techniques in the sport of tennis.  
         [0058]      FIG. 22  shows an embodiment of the sport ball training device  10  of  FIGS. 1-4  and method of hitting a ball with topspin. Creating top spin requires that the user swing a racket from a low to high position as indicated by direction arrows, simultaneously the racket face must achieve a perpendicular alignment to the ground below the ball.  FIG. 23  shows the resulting reaction of the ball sling  14  and ball  12  upon impact with a racquet. When the ball is stuck the ball sling  14  begins to follow the flight path of the ball  12  to which it is releasably secured but is forced to rotate about the axis of the transverse support arm  16 . This causes the loop  22  of the retainer member  20  to stretch and the ball  12  then disengages the loop  22 . The wrapping of the ball sling  14  about the transverse support arm  16  after release of the ball  12  moves the ball sling  14  out of the path of the racquet in order for the s ling to have no significant impact on the practice stoke. The wrapping motion of the ball sling  14  also stores energy in the ball sling  14  during the process that will eventually serve to unwind the ball sling  14  from the support arm  16 . After the completion of the racquet stroke, the spin and flight path of the ball  12  can be observed thereafter by the user. When the device is used on a tennis court the user can readily observe the result of the technique used and make the necessary corrections to the user&#39;s stroke. The device also facilitates the coaching process whereby a coach can stand close to the stroke action of the user and observe and correct the technique based on the observations.  
         [0059]     As shown in  FIG. 24 , after the ball  12  has been struck and leaves the ball sling  14 , the momentum of the ball sling  14  carries it forward so as to wrap itself around the transverse support arm  16 . The ball sling  14  has been wound approximately one and one half rotations at the stopping point with the loop  22  disposed above the transverse support arm  16 . At this point, the resilient recoil force stored in the ball sling begins to unwind the sling from the transverse support arm  16  in a process that is essentially the reverse of the sequence of  FIGS. 22-24  with the ball sling  14  ending the recoil motion in a vertical hanging position ready to be reloaded with another sport ball  12 .  
         [0060]      FIGS. 25 and 26  show the ball sling  14  in use with topspin rotation applied to the ball  12  during the stroke. When ball  12  is struck with a racquet  19  that induces spin on the ball  12 , the release of the ball  12  from the loop  22  is facilitated. After the ball  12  is struck, the ball  12  and ball sling  14  move forward from their nominal resting vertical position hanging from the support device  18 . At this point, the ball is following a flight path direction indicated by arrow  180  and the ball sling  14  is following a curved trajectory indicated by arrow  182 , because, as discussed above, the ball sling  14  is secured to the transverse support arm  16  and is confined to a rotational motion. This causes the underside surface of the ball  12  to press against the bottom section of the loop  22  which stretches both the loop  22  in a circumferential orientation and stretches the sling members  24  and  26  in a longitudinal or axial orientation as indicated by arrow  184 .  
         [0061]     The axial stretching of the sling members  24  and  26  is particularly prevalent in the shock absorbing zones  32  and  46  as this thinner transverse cross section is where the resistance to axial stretch is the lowest. Stretching is also prevalent in the loop  22  where the transverse cross section of the loop element is thin relative to the upper ends  28  and  42  of the sling members  24  and  26 . A gap  186  is created or increased between a top surface  188  of the ball  12  and a top portion  190  of the loop  22  as the loop  22  is stretched from the momentum of the ball  12 . During this process, the ball  12  is also rotating about its own axis from the force of the racquet as indicated by arrow  192 , and begins to move forward with respect to the loop  22 , as shown in  FIG. 25 , such that the center or center of gravity  193  of the ball is no longer aligned with the plane of the loop  22  and ball sling  14 . The rotation of the ball  12  also causes a responsive or counter rotation of the portion of the loop  22  which is in contact with the undersides of the ball  12  as indicated by arrow  194  and causes the ball  12  and loop portion in contact with the underside of the ball  12  to roll away from each other. The portion of the loop  22  which is in contact with the underside of the ball  12  has a substantially round transverse cross which is conducive to the inducement of rotation by the ball  12 . These forces and effects create an unstable linkage between the ball  12  and loop  22  and the ball  12  thus is squeezed out of the loop  22  as it progresses forward along arrow  180  and the ball sling progresses along the curved trajectory along arrow  182 .  
         [0062]      FIG. 27  shows a first step in collapsing an embodiment of the sport ball training device  10  of  FIGS. 1-4  for transportation. The transverse support arm  16  is rotated 270 degrees about clevis pin  82 , which puts it in a vertical position. The locking ring  77  is then released to allow the upper vertical support tube to telescope into the lower vertical support tube  74 .  FIG. 28  shows the second step in collapsing the device  10  for transportation wherein the support legs  66 ,  68  and  70  are moved into a vertical position. Both the transverse support arm  16  and the support legs  66 ,  68  and  70  may be held in position during use by snap lock features of the knuckles  58  and  80  shown in  FIG. 17 &amp; 18 .  
         [0063]     With regard to the above detailed description, like reference numerals used therein refer to like elements that may have the same or similar dimensions, materials and configurations. While particular forms of embodiments have been illustrated and described, it will be apparent that various modifications can be made without departing from the spirit and scope of the invention. Accordingly, it is not intended that the invention be limited by the forgoing detailed description.