Cover 0 is the defense is playing man coverage on every eligible receiver. In the Nickle defense, all 5 DB’s are locked in on a WR/Slot/TE/RB. Whatever the offense sends out, the defense is covering man on man. If it’s base defense, then one of the linebackers will likely latch on to the RB/TE.
The 0 formation can be a powerful tool against a poor O-Line, a quarterback who can’t scramble and/or panics easily, or it’s an obvious run play. With it being 5 on 5 from the secondary, it’s 6 on 6 along the LOS with one of their 6 being the QB that the defense is chasing.
Its downfall is if a Defensive Back blows his assignment and his receiver beats him, you can have an easy TD. They’re also susceptible to crossing patterns and any route that the QB can dump the ball off quickly.
If the OLine actually holds up, or the QB has some good scrambling skills, he can dump off a deep pass and there’s no help deep, or if the QB is a dangerous runner he can make the defense pay, too.
A team needs a great defense like Jacksonville’s to pull this off. Not only does it take at least two good pass rushers like Calais Campbell and Yannick Ngakoue, but the corners need to be close to Jalen Ramsey and AJ Bouye, good. They not only must have the speed to follow on this man play, but know which eligible receiver to cover.
The upside is, it stops the run and terrorizes mediocre quarterbacks. They’re running for their lives or panic and dump the ball off too quickly for a bad pass. This formation, is also known as, crowding the box.
The entire idea is to stop the run, sack the quarterback, or take away the short interior pass.
Good quarterbacks/OC’s can pick a part a defense that tries this too often. This coverage is for special circumstances only. It could be third down, the offense is on the 40, and they need seven yards.
As in any coverage package, a defense can show the quarterback one coverage, but change it at the last second. On this, one or both safeties could drop back at the last second if they think the quarterback is going to try a pass. Defenses often show man and switch to zone, or the opposite. All of it is part of the chess game.
This graphic showcases the man on man function of each of the DB’s locking on one of the receivers. It also shows those not in man coverage are rushing the passer (they can also stop a back in a run play).
Cover 0, Nickel formation
To note* sometimes a player will be a “spy”. They are to watch a certain player no matter what their assignment was. You hear this term often in reference to spying on a mobile QB. They line up like above, but instead of covering, say a slot, they’re actually keying in on the QB to make sure he doesn’t make a run for it.