Question: What is USGA? or Expand USGA?
About the article "Golf", section "Rules and regulations".

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The USGA organizes or co-organizes the following competitions: 
USGA TableOnce the golfer checks his or her course handicap, equitable scoring follows the rules: For example, if a golfer has a course handicap of 8, shoots a score of 83, but that score includes a six on a par 3 (a triple bogey) then the posted score should be only 82.
However, if a golfer with a course handicap of 11 had the same score, the proper score to post is 83.
Note: In other countries, the system of ESC may be different from the USGA system, (e.g., the RCGA system).
When a score is made under a system of ESC different from the USGA ESC system, that score must be adjusted to the USGA ESC system before it is entered as an adjusted gross score under the USGA Handicap System. 
The United States Senior Men's Amateur Golf Championship is a national tournament for amateur golf competitors at least 55 years of age.
It is operated by the United States Golf Association (USGA).
The tournament starts with 36 holes of stroke play, with the top 64 competitors advancing to the match play portion of the tournament.
Golfers must have a USGA handicap index of 7.4 or lower to enter.
The tournament was founded in 1955, expanding on a tournament conducted by the U.S. Senior Golf Association (not affiliated with the USGA), which itself had grown from a senior amateur event at the Apawamis Golf Club in the early 1900s.
Membership in this precursor tournament was limited, so the USGA agreed to start a national championship open to all senior golfers.
Senior Amateur contestants have been permitted to ride in carts since 1969. 
Chambers Bay hosted the 2010 U.S.
Amateur in 2010 and will host the U.S. Open in 2015; these events were awarded by the United States Golf Association (USGA) in early 2008.
Chambers Bay is the longest course in USGA history. 
The ruling authorities of golf, the Royal and Ancient Golf Club of St Andrews (R&A) and the United States Golf Association (USGA), reserve the right to define what shapes and physical characteristics of clubs are permissible in tournament play.
The current rules for club design, including the results of various rulings on clubs introduced for play, are defined in Appendix II of the Rules of Golf.
The overarching principle of club design used by both authorities is defined in Appendix II-1a, which states: "The club must not be substantially different from the "traditional and customary form and make".
The club must be composed of a shaft and a head and it may also have material added to the shaft to enable the player to obtain a firm hold (see 3 below).
All parts of the club must be fixed so that the club is one unit, and it must have no external attachments."
In addition, Appendix II-4a states, regarding club heads, that "the club head must be generally "plain in shape".
All parts must be rigid, structural in nature and functional.
The club head or its parts must not be designed to resemble any other object.
It is not practicable to define 'plain in shape' precisely and comprehensively.
"These two rules are used as the basis for most of the more specific rules of Appendix II, including that no club may have a concave face (1931) and various rules defining what is "traditional" about the shapes of specific clubs, while allowing for the progression of technology.
The "traditional and customary" rule was originally used to ban the introduction of steel club shafts (patented in 1910), as that material was not traditional for shafts; that specific ban was rescinded in 1924 by the USGA (the R&A would continue to ban steel shafts until 1929), and steel would become universal until the development of graphite shafts whose introduction was less controversial.
The "plain in shape" rule was more recently bent to allow for non-traditional driver club head shapes, such as squares, as a compromise to club-makers after imposing and enforcing a 460cc volume limit on these same club heads.
Many recently developed woods have a marked "trampoline effect" (a large deformation of the face upon impact followed by a quick restoration to original dimensions, acting like a slingshot), resulting in very high ball speeds and great lengths of tee shots.
As of 1 January 2008, the USGA and R&A have settled on a regulation that limits the acceptable "trampoline effect" to a coefficient of restitution (COR)—a measurement of the efficiency of the transfer of energy from the club head to the ball—of .830.
Other large scale USGA rulings involve a 1990 lawsuit, and subsequent settlement, against Karsten Manufacturing, makers of the PING brand, for their use of square, or U-grooves in their immensely popular Ping Eye2 irons.
The USGA argued that players who used the Eye2 had an unfair advantage in imparting spin on the ball, which helps to stop the ball on the putting greens.
The USGA utilized John L. Saksun, founder of Canadian golf company Accuform Golf, as a consultant to set up methods of measuring the unique grooves and determining PING's compliance with the rulings.
Saksun, by proposing a cost-effective solution to help PING change the design of subsequent Eye2s, saved PING hundreds of millions.
PING subsequently withdrew their US$100 million lawsuit against the USGA.
Ping’s older clubs were "grandfathered in" and allowed to remain in play as part of the settlement.
Today, square grooves are considered perfectly legal under the Rules of Golf.
However, the USGA has determined that square grooves are illegal in elite-level competition.
According to the USGA, as January 1, 2010, professional golfers on one of the top tours, or those attempting to qualify for one of the three Open Championships, will need to use new conforming wedges (those without square grooves).
Moreover, those who plan to qualify for any other USGA championship will need new conforming wedges by 2014.
In addition, this regulation might include amateur events as well, as a "condition of competition".
Casual golfers may use square groove wedges (and other square-grooved irons) until at least 2024.
Wedges that conform to the new standard are often marketed as "CC" or "Condition of Competition" wedges; this moniker is likely to fall into disuse as players upgrade clubs and the use of non-conforming irons diminishes.