Look on the Slowtwitch main website, and click on Apparel. My understanding is that USAT has a men's top rule, that is, men have to wear one. Just at Kona last weekend for the KKT half, Joe Ackles said in the meeting that he understood USAT's rule but hoped they would give a dispensation, since it can be very hot and some guys prefer to have no shirt to aid evaporation. Although you can get a heck of a sunburn that way. Also, women can't exactly avail themselves of the same opportunity. Anyway, then the USAT official took the mike and said yes, they would not give violations for shirtless men. Hope that helps.

I'm not sure but I believe it's a WTC rule, not a usat rule, so it only affects IM Qualifying races. At any rate, I see shirtless guys at just about every tri I've done(except IMNA races) and I've never heard of anyone being penalized.