Evan Breedlove, a mechanical engineering graduate student at Purdue University who studies neurotrauma in Indiana high-school football players, says that hitting a player in the head is like shaking a Jell-o mold on a platter. The brain shakes, and little splits called microhemorrhages can form. The splits also allow fluid in, which increases the likelihood of further concussions. "It's generally a bad thing when the brain gets exposed to the chemistry in the rest of your body," Breedlove says. The average NFL player sustains as many as 1,500 hits to the head throughout a season. It's the accumulation of impact after impact that does real damage. "The big hit may just be the straw that breaks the camel's back," he says.