There's a lot of ways to build a great defense around an elite player who has multiple dominant traits that allow him to be a versatile piece of the puzzle.
The 2015 Florida State Seminoles built their 10th ranked defense (by S&P) around boundary cornerback Jalen Ramsey. As a great cover corner, Ramsey could allow the 'Noles to roll their safeties down or over to the field while he locked down isolated receivers without help. As a physical tackler and well rounded football player, Ramsey could also allow the 'Noles to bracket an isolated receiver while he helped stuff the run or perhaps blitzed off the edge.
It's not hard to adjust a defense to make the most of an elite talent like Ramsey, who's projected to go in the top 10 of the next NFL draft, but every defense these days has a particular position who will necessarily get isolated and attacked by offenses. A position that, if he provides a major advantage to the defense, can allow them to shut down an offense.
That position is the free safety.
Our definition for who the "free safety" is could change wildly based on the defense and the coverage in question but most teams have at least one position that they primarily use to drop back and be responsible for preventing throws in the seam and then filling the alley against the run. This player generally has to operate in a great deal of space with a lot at stake.
Let's dive in to what this position looks like in different defenses and why the utilization here of a dominant athlete can allow a defense to disarm the most dangerous spread offenses.
The free safety in an aggressive, quarters defense
Because of their success in the Big 10 for the last several years, the Michigan State way of playing defense is increasingly popular around the country, particularly in areas where the offenses can't attack the free safety as easily due to a lack of spread passing acumen.
Many teams will play a space-backer, or a third safety rather than a nickel-corner and deploy him aggressively on the edge to help them outnumber running plays from the offense. The effect is that on any run-action the bracket of the sam/nickel and free safety on the slot receiver becomes de-facto zero coverage in which the free safety is left to cover the slot in wide open spaces:
I've detailed this extensively, most recently when Alabama went after Michigan State's Demetrious Cox in the semifinal. This aggressive approach also runs into challenges when the offense is running something like a zone slice run combined with a bubble screen:
If the field cornerback there isn't playing that block by the Z receiver really well and quickly tightening the space then the FS is in a lot of trouble trying to come downhill fast and at a good angle against a receiver who's usually pretty fast and who's absolutely going to be working in a lot of space.
Then there are any zero blitzes, which have essentially the same effect by virtue of blitzing the linebackers, that also leave this safety to handle a slot receiver in a lot of space. Of course at least now he can count on the pass-rush helping him out:
So, in an aggro-quarters defense where the free safety is having to play in a ton of space on an RPO (run/pass option play), play-action pass to the slot, or on a blitz, this guy needs to have exceptional range, coverage ability, change of direction, and tackling ability to make this work.
Of course if he does, you can build a defense around the aggressive utilization of your field linebacker and completely dominate spread teams who can't make you pay for leaving him isolated in space. If Mark Dantonio ever finds an Earl Thomas then his Spartans aren't going to be much fun to play against.
The free safety in a conservative, quarters defense
We're increasingly seeing teams look to be more conservative with how they utilize their free safety in order to adopt a more "bend don't break" approach to a defense renowned for the way it allows teams to get numbers to stop the run from a two-deep alignment. Many of these teams will still play some "aggro-cover 4" but they'll mix in these more conservative looks as well:
These teams will more often drop the boundary or strong safety down on the opposite end of the field, particularly if they have a good boundary corner who doesn't need deep help, in order to still get the "outnumber the run" effect of cover 4 without being quite as compromised.
These Cover 4 teams are often more cautious with how they utilize their free safety in response to plays like the slice zone/bubble RPO above. They'll have the nickel stay with the slot receiver while the free safety hangs back to see where the ball is going before filling the alley.
On the nastiest types of RPOs that combine QB runs with the forward pass, the nickel is still going to be more concerned with taking away the quick and easy pass to the slot (Y here) and the free safety is going to be asked to clean things up after the fact:
North Carolina tried to play their safeties in a conservative fashion like this and gave up 645 rushing yards to Baylor. It's no joke trying to play bend don't break with so much riding on the safeties' ability to diagnose what's happening, arrive quickly before opposing skill players are running in open, indefensible spaces, and then reliably make the tackle.
However, if a team has the DBs to do it they can make it very difficult for the offense to get any big plays and force them to execute consistently just to get into the red zone. Once the defense is in the red zone, the safeties get aligned closer and closer to the line of scrimmage where they can squeeze the life out of the offense.
The free safety in a MOFC (single deep safety) defense
MOFC (middle of the field closed) defenses, which are generally playing cover 1, cover 3, or are bringing a fire zone blitz, often use either safety as both the down safety and the deep safety. For this article we'll be talking about the deep safety role, which is key to this style of defense.
This role is similar to that of the free safety in a conservative cover 4 defense except that rather than positioning himself on the hash and defending 1/2 the field he's defending the middle 1/3 between the hash marks while the corners and/or nickel/strong safety handle things outside of the hash marks.
Of course, if the deep safety has range to reach plays outside the hash marks, all the better.
In terms of specifics, let's start with that favorite weapon of defensive coordinators, the fire zone blitz, which matches up all of the offense's skill players while dropping the free safety back as an eraser and then bringing a fifth rusher to break down the protection.
That variety of zone blitz asks a lot of the free safety on a play where the offense attacks the seam, like "4-verticals" which attacks either seam and can put the free safety in a two-on-one match-up in the middle. The risk is especially high on a play-action or RPO play where the inside linebackers are sucked in and the safety has to choose carefully what to take away and with less protection from the underneath defenders who can't fill the passing windows:
That ultimate "spread and shred" offense of Art Briles' over in Baylor loves to exacerbate this issue by using extra-wide WR splits so that the FS can't possibly help on both inside receivers because they are too far apart. The challenge becomes how this FS can play deep enough to help over the top against the vertical passing stress while still offering something in run support.
While MOFC coverages are good for keeping the linebackers in the box and accounting for the inside receivers with the nickel and strong safety, they can have problems handling running plays where the linebackers allow a crease.
Because of the wide spacing, the strong safety, nickel, and field corner are unlikely to be able to arrive and make a helpful tackle if the QB hands off. The boundary corner is somewhat nearby but his primary concern is making sure he doesn't give up a deep pass because he doesn't have safety help over the top.
It's on the defense's front six to prevent the RB from getting loose but if he breaks through, it's on the FS to make the open field tackle to prevent six points. What's more, if the QB throws the bubble to the H receiver here and he gets past the DBs out wide guess who's responsible for cleaning things up? That's right, the deep safety, who's other concern is on the other far end of the field.
With great responsibility, must come great power
There's no hiding a slow and ineffective deep safety in the spread era of football. There's too much space and too many options for the offense to attack that position and expose a weak defender. No matter the scheme, a free safety with anything less than excellent range HAS to be protected by excellent players around him who can beat blocks and limit creases and space for the offense to attack.
What's more, he'd better be a film rat who can recognize what the offense is doing and maintain good positioning and awareness of how they'll go after him. You won't always see this cat and mouse game between the free safety and quarterback play out from TV angles but it's an enormous factor in the success or failure of defending spread teams.
It's interesting that we haven't seen more teams, especially in the Big 12 where safeties are regularly abused, opt to move their better DBs to the FS position. Ideally this position would be held by a veteran DB who has excellent range, understands offensive concepts, and is a willing and reliable tackler. For many teams, filling that role would likely require moving one of the better, more well rounded, and intelligent corners inside.
Giving up a good cover corner is an expensive price to pay, but defenses are going to pay the piper for the choices they make no matter what. If they can get this position right they'll have a fail-safe to disarm all the most lethal weapons in the spread arsenal.