Article: Curling
Section: Delivery

Question: What is a typical rate of turn for the stone in the game of curling?

The process of sliding a stone down the sheet is known as the "delivery".
The "skip", or the captain of the team, will usually determine the required "weight", "turn", and "line" of the stone.
These will be influenced by the tactics at this point in the game, which may involve taking-out, blocking or tapping another stone.
 The weight of the stone is its velocity, which depends on the leg drive of the delivery rather than the arm.
 The turn, handle, or curl is the rotation of the stone, which gives it a curved trajectory.
 The line is the direction of the throw ignoring the effect of the "turn".
The skip may communicate the "weight", "turn", "line," and other tactics by calling or tapping a broom on the ice.
In the case of a takeout, guard, or a tap, the skip will indicate the stones involved.
Before delivery, the running surface of the stone is wiped clean and the path across the ice swept with the broom if necessary, because any dirt on the bottom of a stone or in its path can alter the trajectory and ruin the shot.
Intrusion by a foreign object is called a "pick up" or "pick".
The thrower throws from the "hack".
Another player, usually the skip, is stationed behind the "button" to determine the tactics, "weight", "turn", and "line", and the other two may sweep in front of the stone to influence the trajectory (see Sweeping, below).
The players, with the exception of the skip, take turns throwing and sweeping; when one player (e.g., the lead) throws, the players not throwing (the second and third) sweep.
When the skip throws, the "third", or vice-skip, takes his role.
The thrower's "gripper" shoe (with the non-slippery sole) is positioned against one of the hacks; for a right-handed curler the right foot is placed against the left hack and vice-versa for a left-hander.
The thrower, now "in the hack", lines the body up with shoulders square to the skip's broom at the far end for "line".
The stone is placed in front of the foot now in the hack.
Rising slightly from the hack, the thrower pulls the stone back to the toe (some older curlers may actually raise the stone in this backward movement) then lunges smoothly out from the hack pushing the stone ahead while the slider foot is moved in front of the gripper foot, which trails behind.
The thrust from this lunge determines the "weight" and hence the distance the stone will travel.
While not compulsory, most curlers deliver the stone while sliding out from the hack.
Balance may be assisted by a broom held in the free hand with the back of the broom down so that it slides.
The stone is released as the thrower's momentum wanes, or the hog line is approached, at which point the "turn" is imparted by a slight clockwise or anti-clockwise twist of the handle from around the two or ten o'clock position to the twelve o'clock on release.
A typical rate of turn is about 2½ rotations before coming to a rest.
The stone must be released before its front edge crosses the near hog line, and it must clear the far hog line or else be removed from play ("hogged"); an exception is made if a stone fails to come to rest beyond the far hog line after rebounding from a stone in play just past the hog line.
The release rule is rarely enforced in club play unless abuse is suspected.
However, in major tournaments it is strictly enforced; the "eye on the hog" sensor in the stone will indicate whether the stone has been legally thrown or not.
The lights on the stone handle will either light up green, indicating that the stone has been legally thrown, or red, in which case the illegally thrown stone will be immediately pulled from play instead of waiting for the stone to come to rest.