I know he was in the backstroke, the "problem" was that when he turned onto his front (which you can do as early as you like as long as you glide in and don't kick or propel yourself in any way) was that he "front crawl kicked" into the wall, this is clearly against the rules of backstroke swimming. It was made more obvious because Piersol turned slightly earlier and spent more time on his front than the others did, making the error more obvious. If the NBC commentators chose to "miss it" I wouldn't be suprised, but the BBC commentators pointed it out and the slo mo was definative.The race in which Piersol was questioned was the backstroke - not the front crawl. And the issue wasn't his kick; it was whether he flipped over onto his stomach too early on his turn (which, if done, would have slowed him down anyway). No one could detect that in the replays
As I said both Kitajima and Piersol commited acts that should have DQd them, neither was, such is life, the results stand. I tend to agree with Piersol's coach that it could very well have been a reaction to his critisism of Kitajima's action, maybe he'll learn the lesson that it's better to keep your mouth shut on matters that don't concern you until after you've competed faultlessly yourself.