You'll probably hear outrage on your pool deck if one of your best swimmers gets DQ'd at a meet. He/she couldn't have done whatever the DQ stated, people will say, because he/she swims year round.
I mentally roll my eyes when I hear this, though I do understand. At a dual meet a few years ago, my then 13-14 swimmer got DQ'd for a one hand touch on the fly to back turn in the IM. I was flabbergasted, but I was also the starter, so I couldn't do more than make a note to ask my son after the meet. His response? Oh, yeah, it happens more times than you think.
I was watching the Olympic Trials 100 breaststroke prelims on Sunday, courtesy of NBCOlympics.com, when I heard the announcer say one of the swimmers had been disqualified for a one hand touch. Yes, at the Olympic Trials. Those turn judges at the ends of the lanes and the stroke judges walking the sides aren't just there for decoration. Even good swimmers can make mistakes. They are in a bit of a hurry, after all.