Blitzing is when 2 or more linebackers or defensive backs attack the line of scrimmage.

Blitz, short for the german word "Blitzkrieg", means "lightning war". Our job when we blitz is to add as much conflict and chaos to the offense as possible.

When And Why We Blitz
Blitzes can be called on any down. It's important to study the opponent's offensive tendencies, so we can make sure our blitzes are effective. For example:

Blitzing On Passing Downs
Typically, 3rd and long forces teams to throw the football downfield. For teams that don't often throw the football, this can be a nightmare scenario having to put the ball through the air. It's in our benefit to adding even more pressure to the quarterback, to make a mistake

However, if the team is a pass-happy, with a quarterback who throws the ball a good amount, blitzing needs to be used as a means to disrupt, not fluster.

When studying tendencies, if a team likes to run sprint-out on 2nd/3rd and short, it's our benefit to blitz off the edge to make the quarterback pull up and throw the ball earlier. This is prime disruption, based on offensive tendencies.

Run Blitzing On Running Downs
Similar to how we disrupt the pass with the blitz, run blitzing can be just as effective.

For a team that likes to pull guards or pre-determine their blocking assignments, adding a last-second rusher will typically cause confusion or allow for an open tackle.

For example, Wing T offenses are known for pulling guards where the ball is going. Penetration through the pulling guard gaps could potentially score a clean run through with a linebacker.

When Don't We Want To Blitz
Blitzing is great on both running and passing downs. Causing confusion, disrupting run/pass blocking schemes, and making a quarterback uncomfortable is great, but what happens when the offense starts to figure out your blitzing tendencies?

Whether you're blitzing (6 man pressure) or running a dog (5-man pressure), there's a good chance your defensive back's are in man coverage.

Man coverage is one of the hardest techniques to play in football. Especially covering receivers in the slot. If a blitz gets picked up properly, having a fast receiver running vertically or across the field on a slower defensive back may be trouble.