Rule 15-1
Changing golf balls during a hole or a stipulated round
Q.May a player change golf balls during the play of a hole or a stipulated round? When the player is permitted to substitute another golf ball may he change to a ball of a different brand or type?
A.Rules 15-1 and 15-2 explain that the player must complete play of the hole with the ball with which he began the hole unless he is proceeding under a Rule that permits him to substitute a ball. The player may change balls between the play of two holes as well.
Rules 26-1 (Water Hazard Rule), 27-1 (Ball Lost or Out of Bounds) and 28 (Ball Unplayable) are examples of Rules that permit the player to substitute another ball. Rule 5-3 permits a player to substitute another ball during the play of a hole when his original ball has become unfit for play during the play of that hole. Other Rules (e.g. Rule 18, Rule 24, and Rule 25-1) permit the player to substitute another ball only if the original ball is not immediately recoverable.
Note that Rule 16-1b, the Rule that allows the player to lift his ball from the putting green, does not permit the player to substitute another ball; this precludes the player from substituting a “putting ball.”
A player who substitutes another ball when not permitted to do so incurs the general penalty (loss of hole in match play or a two stroke penalty in stroke play) under the applicable Rule. For instance, a player taking relief, without penalty, under Rule 25-1 due to interference from ground under repair is required to do so with the original ball (unless it is not immediately recoverable). If that player substitutes a ball (and makes a stroke with it) when his original ball is immediately recoverable he incurs the general penalty under Rule 25-1 (as it is the applicable Rule in this case).
When changing balls, the player is permitted to substitute a ball of another brand or type unless the Committee has adopted the One Ball Condition of Competition (see Appendix I; Part C; Section 1c). This optional condition (usually referred to as ‘The One Ball Rule’) is generally adopted only in events that are limited to professional golfers or highly-skilled amateur golfers. Generally, this condition of competition is not adopted in club-level competitions.
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I guess that WGT is going on the part of the rule that says that you must finish the hole with the same ball that you started unless as the rules say you hit into a hazard and the ball could not be retrieved, or it was lost.
The confusion is that the PGA operates under different ball rules than does the USGA. In the PGA you are required to finish each round with the exact brand and type of ball that you started the round. For example if you start with a Titleist Pro V1 you must finish with a Titleist Pro V1, you can not switch to a Callaway ball for example during the round.
I think the original comment was in request to a ball counter. The OP was discussing the issue of having a ball in your bag. It could be one that has been hit once or 100 times and it is not possible to know how much play is left. Once you start the game you can see an estimate of the life but you still don't know if you can finish the round with it.
This is especially frustrating when you are trying to clean out your inventory of balls or have switched to a new ball and want to use up the old ones, even if they only have a difference of the vapor trial or color you still can't use them.
It's a legitimate question and since the ball life bar is there, I have to think that WGT knows exactly how many hits are left and could tell the players.