Two basic premises underlie the USGA Handicap System, specifically that every player will try to make the best score at every hole in every round, regardless of where the round is played, and the player will post every acceptable score for peer review.
It is ultimately the player's responsibility to make sure that every acceptable score is posted. Every acceptable score must be adjusted if a hole score exceeds the ESC (Equitable Stroke Control) maximum number allowed for your Course Handicap, if you began but did not finish a hole (Most Likely Score, Section 4-1) or if you do not play a hole or play it other than under the Rules of Golf (Holes Not Played, Section 4-2). If you happen to play in an event and the Committee conducting the event tells you that they will post the score for you, it is your responsibility to post the score if the Committee fails to do so.
Comments on Acceptable Scores - We often hear that players do not believe that they should post a score because they were playing a practice round or that they were playing in a Four-Ball (More commonly known as 2-Person Best-Ball) event and that they play different in those scenarios. We have yet to find the words "Practice Round" in the USGA Handicap System. Please remember that one of the premises behind the USGA Handicap System is that you will make every effort to make the best score at every hole in every round.
A Comment on Unacceptable Scores - We have been asked why the USGA no longer allows a person to post a score for a round if they play alone (Unaccompanied). One of the major backbones to the USGA Handicap System is peer review. How can you provide peer review for a round, which you cannot support, or dispute scores that have been posted to a player's scoring record? The USGA believes it provides a more accurate view of a golfer's ability, supporting integrity, fairness and equitable play among all golfers.
USGA Handicap Index - Is a measurement of a player's potential ability on a course of standard playing difficulty. Ideally, it is based upon the best 10 Handicap Differentials in the Player's last 20 scores. If you have less than 20 scores in your membership record the number of Handicap Differentials used is less than 10. Your USGA Handicap Index is not based upon your average score or average Handicap Differential.
Equitable Stroke Control - Reduces high hole scores for handicap purposes only in order to make handicaps more representative of a player's potential ability.
Most Likely Score - Is the score a player must post for handicap purposes if a hole is started, but not completed or if a player is conceded a stroke. The Most Likely Score consists of the number of strokes already taken plus, in the player's estimation, the number of strokes it would take the player to complete the hole from that position more than half the time. Your ESC maximum does not automatically become your Most Likely Score.
Holes Not Played or not Played Under the Rules of Golf - If a player does not play a hole or does not play it under the Rules of Golf (Except for Preferred Lies/Winter Rules), the score used for handicap purposes must be par for the hole plus any handicap strokes the player is entitled to receive on the hole. Two examples of holes not played under the Rules of Golf would be taking a mulligan or using automatic two putts.