Watching high-performance athletes, one sometimes can observe unusual facial phenomena that the athletes would never do normally, but during the heat of battle do with gusto. It's interesting to note that many of the very best athletes have these muscular contortions, so the question is why.
There are three contortions that involve the mouth. Michael Jordan, who many consider to be the best basketball player ever, was famous for sticking out his tongue as he raced down the court preparing to go airborne for a monster dunk. Jordan's fame was so great that schoolyard players took to imitating the tongue-wag, perhaps thinking it was done by Jordan out of bravado and not an unconscious act. In squash, the great Peter Nicol would often be seen demonstrated another mouth phenomenon, known as a rictus, in which the lips are pushed tightly backward in what looks like a half-smile, half grimace. Opponents knew that if Nicol had that look he was fully concentrating on the task at hand, and that spelled trouble for them.
The third possible mouth contortion is biting the lip, as one sees most often in children who are concentrating intently on something. (Another profession that shows its share of facial tics: professional musicians, such as pianists and violinists, where lip biting and rictus are more popular than tongue wagging, since licking your violin while you play may be problematic.)
So why does this happen? These actions are all examples of motor overflow or motor disinhibition, in which the athlete's capacity to direct their overall motoric response to the circumstances at hand is diminished. A pictorial representation of the part of the human brain that directs movement and motoric information to the rest of the body is called a cortical homunculus (above), a fancy name for a drawing that proportionately relates a body part with the motor cortex of the frontal lobes of the brain. Thus, the legs are represented in superior regions, while the arms are below the legs, and the neck, brow, eye, lips, jaw and tongue descend from there. These relationships vary individually, and also change with age, but the topographical drawing is useful for neurologists and other clinicians studying the brain.
Are you still with me? (Are you biting your lip perhaps?)
Motor overflow occurs when an athlete is working exceptionally hard physically and mentally, necessarily exerting extensive control over superior and medial regions (i.e., the legs, arms, and hands) and temporarily 'disinhibiting' regions where control isn't particularly necessary for the task at hand, a dunk, say, or a crosscourt shot to the nick. The disinhibited regions result in movement of the face, lips, and tongue.
There are many top athletes who don't exhibit motor overflow, of course, so there is nothing to suggest that only the very best of the best show motor disinhibition. But I think one can say that of those athletes who do show these signs it is wise to be careful when playing them if the tongue comes out, the rictus starts smiling, or the lip gets bitten.
Because you are about to lose....