Because I heard it mocked in Letterman's interview with David Wright the other day and saw it referenced in several blogs regarding Mike Pelfrey, I thought I'd share an excerpt from a conversation I had with a former major leaguer in regards to, for lack of a better term, this tongue-sticking-out thing. I don't have the background in physiology to confirm that his words are accurate, but I'm trusting of them.
To paraphrase what was told to me:
It's good that they do that...Almost every pro athlete does it in some way...remember Michael Jordan? I used to wonder after I'd play why my tongue would hurt after a game...It was explained to me that by sticking out your tongue, you're relaxing your body. You know that if you clench your teeth, you tense up, and your muscles all tense up too. That's why someone like Roger Clemens wears a mouthpiece, because he doesn't want to clench his teeth Sticking out your tongue releases that tension. It allows you to maximize your muscular effort.
True Metgues know...That the athlete I'm paraphrasing never had a walk-off hit for the Mets, nor did he have a walk-off win for them. Of course, he never played for the Mets, so that's a pretty crummy hint.