There are some parts of the quarters coverage scheme that are universal, one difference you will see is where defenses line up their strong side curl-flat defender versus “two detached” formations.
A team like Michigan State that plays with mostly base personnel will use a linebacker to midpoint the #2 receiver and the end man on the line of scrimmage.
This alignment can create a conflict versus play action. In Michigan State’s quarters scheme the Sam linebacker is responsible for a gap in the run game but also to collision #2 and play the curl-flat area. Because Sam is tied into the box he must respect the play action fake. With #2 already having outside leverage, once the Sam steps to the fake it opens up a big window to throw the speed out.
Ends up as an easy 13 yard first down completion for the offense.
Defenses like Alabama’s use a 4-2-5 alignment versus two detached formations when in quarters, to take away those types of easy throws. Bama will go with 5 defensive backs in quarters and align the strong safety outside #2.
The strong safety is the curl-flat player in coverage, but he’s not tied into the box. The strong safety’s run responsibility is “force”, meaning he has outside contain and must turn everything back inside to the free safety and pursuit. Because the strong safety has force and is not tied into the box, he does not have to come up hard on a play action fake like the Michigan State linebacker did.
Not only does this alignment take away the speed out that was thrown against Michigan State, but it also makes it nearly impossible for teams to throw the popular bubble screen. #2 isn’t an option at all on the bubble due to the position of the strong safety. Auburn tries to throw the bubble to #3 but it’s very difficult to gain the edge versus this defensive alignment.
Already having outside leverage on #2, the strong safety is able to fight the block from the outside in, turning the play back inside to the free safety who is filling the alley.
The bubble screen goes for a minimal gain of a couple of yards.
Now I know some people are going to wonder if playing the strong safety outside of #2 is going to leave you vulnerable in the run game. If your safeties are trained properly you still have strong run support. Here is an example: Bama is in quarters again, SS aligned outside #2, Auburn dials up a jet sweep.
With the strong safety playing his force responsibility and taking on and fighting the block from #2 from the outside in, it forces a cutback. The free safety buzzes his feet until he can diagnose the run play. Once the free safety reads it, he comes downhill immediately. Knowing that he has the strong safety playing force and pursuit help from the inside, it allows the free safety to attack aggressively, rather than worrying about taking the right angle.
The free safety makes the tackle for no gain.
Both Michigan State and Alabama were playing the same coverage, but you can see how some subtle tweaks in personnel and alignment in a quarters scheme can make a huge difference.