Four-man Best Ball Rules
In the popular best-ball format, all four players on the team play each hole as they would in a normal round of golf. The normal USGA rules of golf apply. There is no "best ball" involved. Each player plays his shot for the best possible score. When the hole is completed, only the best score for the hole is added to the score card. As an example, if on the 10th hole the individual scores were 4, 5, 5 and 6, the hole would be scored as a four for the team.
USGA Rules Apply
In a four-man best ball format, all USGA rules apply since each player completes every hole. Since many four-man best ball tournaments are fundraisers, there are usually some rule exceptions to make the game fit the purpose. One of the most popular is the mulligan, which is a probably the most popular additional charge item at any charity tournament.
There are many variations to the four-man best ball format. The scramble is one of the more popular variations. In this format, all players tee off and the team (usually the captain) selects the best shot. The other three players pick up their balls and move to the position of the best shot and the process repeats. If you are playing in a tournament, the organizers will probably have a handout that will explain any specific exception rules that apply. Two popular exceptions are: not allowing two consecutive shots from the same player and requiring that each player's tee shot be used the same number of times.
Additional USGA Rules
There are many USGA rules that deal specifically with four-man best ball play when there are additional simultaneous matches taking place among the four golfers. These rules are more related to club-sponsored tournaments and are administrative in nature. They can be found in the USGA Rules section 30.