across the line of scrimmage or otherwise engage any of the offensive players. Once an opposing offense has broken their huddle and lined up in their formation, defensive players often call out instructions to each other to make last-second adjustments to the defense. Run defense To prevent the opposing offense from gaining yards on the ground, a defense might put more emphasis on their run defense. This generally involves placing more players close to the line of scrimmage to get to the ball carrier more quickly. This strategy is often used when the opposing offense only needs to gain a few yards to make a first down or score a touchdown. Pass defense When the defense believes the opposing offense will pass the ball, they go into pass defense. There are two general schemes for defending against the pass: Man-to-man, where each eligible receiver is covered by a defensive back or a linebacker. Zone, where certain players (usually defensive backs or linebackers, though occasionally linemen as well) are assigned an area on the field that they are to cover. Blitz There are times when a defense believes that the best way to stop the offense is to rush the quarterback, which involves sending several players charging at the line of scrimmage in an attempt to tackle the quarterback before he can throw the ball or hand it to another player. Any player on the defense is allowed to rush the quarterback, and many schemes have been developed over 50 years that involve complicated or unusual blitz "packages". Specific defensive strategies Defensive strategies differ somewhat from offensive strategies in that, unlike offenses that have very specific, detailed plans and assignments for each player, defenses are more reactive, with each player's general goal being to "stop the offense" by tackling the ball carrier, breaking up passing plays, taking the ball away from the offense, or sacking the quarterback. Whereas precision and timing are among the most important parts of offensive strategy, defensive strategies often emphasize aggressiveness and the ability to react to plays as they develop. Nevertheless, there are many defensive strategies that have been developed over the years that coaches use as a framework for their general defense, making specific adjustments depending on the capabilities of their players and the opponent they are facing. Some of the most commonly known and used defensive strategies include: Man-to-man Coverage shells (cover 2, cover