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Seems to me I remember the PGA about 1975 or so, at Medinah, with John Mahaffey and Lou Graham battling to win on Sunday. They get to 17, about 215 over Lake Kadijah (back then), and Mahaffey pulls out a Top-Flite to play the hole, makes par and wins the PGA.
I think, but I'm not sure, that this was the beginning of "the 1 ball rule". Does anyone know if this is true?
MinnSkinny

...... what's a 1 ball rule?

i think you mean a person has to use the same ball all game, well players can switch balls between holes but it has to be the same brand and exactly the same ball, and during the hole a ball cannot be changed

Right, normal tournament rules restrict players to the same ball type, to be played throughout the round. Thus, the One Ball Rule. My friend says Billy Mayfair now is an automatic endorser.

The One Ball Rule is in Appendix A (Local Rules) - Part C (Conditions of the Competition) - Section 1 (Specifications of Equipment) of the rule book under Conditions of the Competition. It says, "The following three conditions are recommended only for competitions involving expert players." The three rules are:

1. List of Conforming Driver Heads - limiting drivers used to those on the conforming driver list.
2. List of Conforming Golf Balls - limiting balls used to those on the conforming ball list.
3. One Ball Condition - prohibit changing brand and type of ball during a round.