Used primarily by stronger defensive tackles, the bull rush is a simple technique that can be expanded to include more precise technique. Many defensive line coaches teach the bull rush, but do not allow their linemen to practice the it during drills, because of the lack of technique required to execute it. Power and explosion are the only requirements of a good bull rush, and many young players do this naturally.
The key to a successful bull rush is leverage. You cannot bull rush standing straight up. Your helmet must be lower than your blocker's helmet. Speed rushers try to reach the quarterback by running around the pocket, and without a bull rush coming from the middle of the line, the quarterback can step up in the pocket and throw the ball. Push the pocket backwards, collapsing the space that the quarterback needs to throw the ball or escape.
Where you place your hands can make the difference between merely collapsing the pocket and sacking the quarterback. You will be lower than your opponent so that you have leverage. Drive your hands up and into the chest plate of your blocker's shoulder pads, grabbing the outside edges with your thumbs pointing up. Push with your arms to extend the defender to an arm's length. Hand fighting is a common activity for defensive linemen. Both you and the offensive player want your hands and arms on the inside of the offensive lineman's pads.
Although it is true that most bull rush artists are defensive tackles who use brute force to push the pocket backwards, several defensive ends have begun using the bull rush as a counter move against offensive tackles who are overplaying their speed rush. After several attempts to run around the edge of the offensive tackle you sprint upfield at the snap at least two steps, though some ends will take four steps because of a smaller stride length. Planting on your outside foot you convert what looks like a speed rush into a bull rush by running directly at the offensive tackle's outside armpit. This direct path should allow you to collapse the pocket. An added benefit to this technique is that you often have at least two or three steps to build up to full speed before you collide with the tackle, who must stop his backward momentum and is likely stationary on contact.
Any pass rush technique can be stopped, and the bull rush is often the easiest to defeat, especially if you know that it is coming. However, in order to stop a strong bull rush, an offensive lineman must overcommit himself, providing openings in several other areas. If your momentum stops during your bull rush, slide to either direction and turn your hips into the lineman slightly. Quickly and violently pull the lineman past you before continuing to the quarterback. Another option is to spin, most likely to the outside of the lineman. Simply swing your inside leg around behind your body, turning your back to the lineman. As you turn, squat lower to improve your balance, and violently swing both arms. Your inside arm will increase the speed of your spin, while the outside arm will cross between you and your blocker, knocking his hands off of you in the process.