I like the warning system or yellow card idea.

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I'll be what I am
A solitary man

one_lap - just wanted to double-check. Did you see the referee's list, posted at the race by the results (and sometimes online), or just the penalty time on the website's results page? If it was just the time, don't assume it was drafting. They use the same time for blocking, passing on the right, littering, and wearing an MP3 player. You can get the exact penalty and what was written up about it by getting in touch with the lead referee - the race director should be able to provide you with contact info.