Jon thunk about Football: Defense Personnel and Jobs

Welcome to Jon thunk, where I, Jon Crain, think about things and write about them in a hopefully interesting way. My sources are Google and Wikipedia mostly and I won't be citing them except as sources of further interest for nerds like myself.

Today, I'll be thunking about Football Strategy. As I'm American, I'll just assume the rest of the world knows I'm talking about American Football.

Let's start with personnel, who you choose to put on the field. You get eleven players on defense, putting the right people in is the first step to achieving greatness. For defense, there is one main continuum, the strength-speed trade-off. Bigger beasts hit ball carriers harder, and can move past blockers more easily, but also are inevitably slower. Faster fellows can more easily cover pass plays, by running fast and jumping high, and won't do as good a job going through an offensive lineman. So typically you'll have players that are built for the job they have to do.

Beginning with the big-strong side of the spectrum, we have defensive linemen. They have a few jobs to do and normally you'll put three or four of them on the field. If it's a pass play, their job is to pressure the quarterback, and possibly knock down passes by getting their hands up with the quarterback throws. So, they need to be big and strong, but not as fast as other defensive players. Ideally they also have awareness to spot the ball, to either be able to tell whether it's a run or a pass, and get their arms up with the QB is going to throw. Also, the intelligence to know when to try to club the ball out of the QB's hands. On a run play, they need to get around or through their blockers and tackle the ball carrier. Injury resistance is a big factor here, they undergo the most force on any given play and so need to be tough and lucky. They do need to be faster than, say, an offensive linemen as they need to get to the QB quickly, so they'll be the biggest on defense but smaller than an offensive lineman.

The more likely you think the opponent is to run, the more of these guys you want to put in, as they rarely cover any receivers downfield, but are pretty good at stopping the run.

Moving towards the middle of the spectrum, we have linebackers. Normally you'll have one to three linebackers. They may aid in the rush attempt on a QB during a pass play, but more typically they need to quickly identify if the play is run or pass, and then either collapse for a run, or cover tight ends for a pass. They need to be big enough to cover a tight end, and fast enough to cover a receiver and run down ball carriers. They need to hesitate just long enough to identify a run or a pass, and then commit.

Moving a little towards the fast side of the spectrum, we have safeties. They have similar builds and jobs to linebackers, but ideally are a little faster as more often they are going to help out corners on pass coverage. On a predicted run play, we're going to put in more linebackers, on a predicted pass play, more safeties. In the case where the opponent is for sure going to pass, we might even put in corners at the safety and linebacker spots. They need to hesitate a bit more than linebackers before they make a decision on run vs pass, because if they get it wrong there's no one behind them to cover.

And finally, the speedy end of the spectrum, corners. They rarely rush, and their main job is to directly defend against fast receivers. They also need to be able to jump high as receivers are often taller than them. They also are responsible for helping in a situation where the offense wants to run to one side of the field, so they still need to identify run vs pass, but can err on the side of pass protection.

Your main job in terms of personnel is ensuring there are no obvious mismatches. For example, if your opponent has a two tight end set and you only have one linebacker, it's going to give the offense opportunities to throw over your corners, or tight ends to get the ball quickly and bowl over your corners. If your opponent has a five wide receiver set and you have three linebackers on the field, you're going to have trouble defending the pass.

One interesting quirk here is that the defense cannot substitute unless the offense does. So it's really important you get the right people out there, because the offense can go hurry up and lock in mismatches, at least until they get too tired to function. And because in general the offense is smaller than the defense, they likely won't get tired first, compounding the advantage of hurry up.

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