He can call for linemen to rush differently, linebackers where to go and what pass defense to run. Examples Run prevent. This is a way the defense uses extra linemen to stop the run. The defense expects running plays and commits players to the run. A team faces an opponent that runs the ball alot will use this style.
Defenses expect a team to pass.
Many times near the end of the game if the offensive team needs to score quickly they will pass on every down. Defenses like to use this prevent style which includes extra defensive backs. Zone Pass Defense. This is a pass defense where the defensive backs go to a zone or area on the field. They cover the player that comes into the zone.