Let’s talk about Pass Defense. This doesn’t pertain to defending against Screen passes, since the purpose of screens is to stop you from focusing on Passes.
First, focus on PASS! Linemen are blasting forward, heading toward the QB, and linebackers are immediately dropping back into their zones or following their man, unless they’re blitzing. Have your line Stunt (on the shift screen) to increase your pass rush.
If the offense has extra wide receivers, you should usually respond by bringing in your Nickel (or even Dime/Prevent).
There are two components to stopping the pass – the pass rush needs to harass the QB and hopefully sack him before he can complete the pass, and the coverage needs to keep the receivers covered so the QB can’t find an open receiver.
Knowing this, you can increase the pass rush with blitzes (which requires Man coverage) or bring in extra defensive backs to help cover the passing areas.
Four-man lines usually put more pressure on the QB than three-man sets, unless you have a 3-4 with Zone coverage. In the 3-4/Zone defense, the weak side linebacker charges in.
Against short passes, the 3-4 is best, then the Nickel. Against medium passes, go with Nickel. Prevent gives up short passes and some medium ones, but can cause more interceptions and and are tough on deep routes.
COVERAGE. Man-to-Man is the best against Screens and short pass routes. If your personnel are excellent, it can also be very strong against medium and deep passes, but is more risky. Short Zones are the best against medium passes, while the 3-Deep Zones work best against long passes.