A definition:

A concussion occurs when the head hits or is hit by an object. A concussion can also occur when the brain is pushed against the skull with a strong force. In such cases, parts of the brain that control mental function may be damaged. The injured person may become disoriented (confused) and may briefly lose consciousness.

The U.S. Centers for Disease Control and Prevention (CDC) estimates that about three hundred thousand people experience mild to moderate concussions each year as a result of sports injuries. Most of these people are men between the ages of sixteen and twenty-five.

See illustration 1.A below:

For more information, the Library of Congress recommends that you find your local Rey Maualuga. Anger him; this may be done by staring directly at him or at a picture of him, breathing oxygen in his vicinity, or even standing too closely to him in days that end in "y." Then wait behind as many blockers as you like for desired results. He'll find you.

(BTW: What in the hell is wrong with UCLA's protections? Olson was sacked five times in the game against Utah. West coast offense short pass three step drop quick protect whaAAAA?)