A blitz is when a defense sends more pass rushers than its standard four. The extra man comes from somewhere else, usually a linebacker or a defensive back, and someone he would otherwise have covered is left uncovered.
The Trade-Off
That is the whole thing. Rushing five gets to the quarterback faster, but it leaves six defenders to cover five receivers instead of seven. Rushing six leaves five on five, with no safety help anywhere.
A blitz that arrives late is worse than no blitz at all, because the quarterback throws into the space the blitzer left.
Common Types
Fire zone. Five rushers with three deep and three underneath behind them. A lineman drops into coverage while a linebacker rushes, which confuses protection assignments.
Corner blitz. A cornerback comes off the edge, usually unblocked because the offense does not expect it. High risk, since his receiver now has no one on him.
Safety blitz. Same idea from deeper, which gives the offense more time to see it but disguises it longer.
A-gap pressure. Linebackers threaten the gaps either side of the center before the snap, often without both actually rushing. The threat alone changes the protection.
Zero blitz. Everyone in man coverage, no deep safety. Maximum pressure, maximum risk, usually reserved for obvious passing downs or desperation.
How Offenses Answer
Quarterbacks read the front before the snap and slide protection toward the threat. A hot route sends a receiver to a quick spot so the ball can come out before the rusher arrives. Screens punish a blitz directly, since the rushers take themselves out of the play.
Why Teams Blitz Less Than You Think
Analytics have pushed defenses toward generating pressure with four and covering with seven. A defensive line that can win one on one makes blitzing unnecessary, which is why elite pass rushers are paid the way they are.
Related
The nickel defense · Cover 2, 3 and 4 explained · All football positions
The Bottom Line
Extra rushers, fewer defenders in coverage. It works when it arrives quickly and is punished badly when it does not.