Golfers playing in a professional tournament are not held under any special regulation that limits the number of balls that they can have in their bag to use over the course of the round. For this reason, it is advisable that a player bring more balls than they think they will need, as running out of balls leads to a disqualification.
While there is no limit on the total number of balls that a player is allowed to bring onto the course with them, there are still restrictions on the number of brands and styles of ball that a golfer may use. Golfers are not permitted to use two different styles of balls in one round, meaning the ball a golfer tees off with on the first hole must be the same type of ball that is used in every stroke. This prevents players from using balls geared toward distance on long holes, and high-spin balls on short holes.
Changing Balls Mid-Hole
In addition to playing the same type of ball for every stroke of a round, a player must also play every stroke on a hole using the same ball as long as that ball remains in playable conditions. Changing balls illegally will lead to a penalty for the player, which varies depending on if they are playing stroke play or match play. A player is permitted to change their ball if their ball is damaged, however, such as a ball which strikes a rock or path and suffers a chip or gash in the casing.
Size and Weight
The type of ball chosen by the golfer for a round must also be deemed a legal ball according to USGA standards. These regulations include limits on the maximum weight of the ball, as well as the minimum diameter. A golf ball may weigh no more than 1.62 ounces, as a heavier ball can be hit farther. Additionally, a ball may not have a diameter of less than 1.68 inches, as a smaller ball will be easier to get in the hole on the green.
A ball can also be deemed illegal due its composition, which can be used to manipulate the ball's flight distances or spin.
Every golf ball that is manufactured by a leading golf ball company is tested to ensure that it does not have rule-breaking characteristics. The initial velocity of all balls is tested in a controlled environment. The speed of the ball at impact is measured, and if it exceeds the legal limit, the ball is not approved. Similarly, balls are tested for carry (the distance traveled in the air) and run (the distance traveled after first contact with the ground).