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is conforming club that is purpose designed to be a swing aid/trainer illegal to use and swing during a stipulated round?
Answer - No. There is no 'illegality.' A conforming club is a conforming club. As long as it is one of no more than 14 of 'em. Perfectly legal. Doesn't matter what it was "designed to be." (Trainer or otherwise.)
You sure?
4-3/10 Use of Training or Swing Aid During Round
Q. During a round, may a player make a stroke or a practice swing using a club with a weighted headcover or "donut" on it, or use
any other device designed as a training or swing aid?A. No. The player would be using an artificial device to assist him in his play in breach of Rule 14-3, but see also Decision 4-4a/7 for use of a weighted training club.
4-4a/7 Carrying Weighted Training Club
Q. May a player carry a weighted training club in addition to the 14 clubs selected for the round?
A. No, but a weighted training club may be selected as one of 14 clubs carried by a player, provided it conforms with Rule 4-1 (e.g., an excessively-weighted driver head may breach the limit on Moment of Inertia — see Appendix II).
So, that makes for some real gray area in the rules. Can a club be both conforming with the rules AND purpose built as a training club? And if so, which rule applies? After all, Decision 4-4a/7 only says the player can carry the club, not use it. Put it this way, the question has two right and two wrong answers. I've been a rules official in small events in the past, this is not a decision I would want to have to make.