A bull rush in football is a technique used by pass rushers, including linemen and sometimes defensive ends, to beat blockers protecting the quarterback. The bull rush is an approach that relies on raw power, as opposed to other pass rushing techniques that make more use of quick hands and deft footwork.
The bull rush is effective when used by defensive linemen as other pass rushers surround the pocket. With an offensive lineman being pushed right at him, ideally, the quarterback will have nowhere else to go.
In short, a pass rusher using a bull rush technique is quick off the line of scrimmage in order to charge directly into his counterpart on the offensive line. He uses both arms to attack the offensive lineman head on in order to drive him back directly toward the quarterback.
The bull rush technique requires the pass rusher to first get lower than his opponent in order to create leverage. Then, he must shoot his hands into the chest of the offensive lineman, doing his best to keep them on the inside of his opponent's frame and his arms extended. When using this technique, the pass rusher should make sure he has a solid base with his knees bent and body forward. His feet should be constantly moving as well.
After the pass rusher has pushed the blocker back far enough, the pass rusher can use another technique, such as the swim move or rip move in order to actually reach the quarterback. At this point, the passer can be sacked, or at least further pressured.
When facing a bull rush, a blocker should do a few things to effectively defend against it. First, he should set his feet in order to hold his ground. He should also keep his arms bent slightly so they remain strong enough to hold off the pass rusher. Finally, he should refrain from bending his knees at a 90 degree angle or greater so he is not thrown off balance.