Steelers quarterback, Ren Roethlisberger, already suffered two concussions this year, but quickly bounced back on the field.
Younger athletes are not that much different.
Most athletes shrug off a bounce of the head, so they can get back in the game.
Concussions can be hard to diagnose, but now a computer test is taking out some of the guesswork.
A doctor at the University of Pittsburgh developed the test to diagnose concussions. "When they go back too soon we can see very negative effects on brain function if they are hit again," Dr. Mark Lovell of the University of Pittsburgh explains.
Among the exercises, athletes memorize a series of words and designs and recall them later.
About 1,500 high schools, colleges and professional sports teams use the test, which is called Impact.