The Prevent Defense

I submitted this question to Cecil but was rebuffed with the suggestion that I post it here as someone may be able to offer an answer. Here goes:

Every football fan knows the scenario: your favorite team is up by 7 points or less late in the fourth quarter. Instead of playing the game out with the same defensive strategy, your team’s coaching staff elects for the dreaded “prevent defense” where they rush fewer players and drop more into pass coverage in order to stop a huge passing play. Invariably the opposing team goes the length of the field in three or four plays, scores a touchdown, and your team loses, leaving all fans moaning about how the only thing the prevent defense prevents is a win.

My question: is there any hard statistical evidence that proves the prevent defense works more often than it fails? Is this a situation where fickle fans only remember this strategy when it fails and quickly forget it when it succeeds? Or is this some flawed piece of conventional football wisdom that is followed more through tradition rather than through any data that suggests it’s the statistically
sound way to hold a slender lead?

I’ve charged a friend of mine who does market research to study every televised college and professional football game since 1990 and get back to me with a definitive answer. He hasn’t gotten on board with the project with the enthusiasm I had hoped, so I’m turning to you. Please help.

I think the answer you’re seeking is in the middle paragraph. Unfortunately, I can’t confirm or deny it. You’d also have to judge whether or not the same Prevent defense is being run, which I would think it wouldn’t. Is the defense rushing 2? 3? 4? Is there any bearing on the results any way?

I’m curious as to what you would consider “success” and “failure.” It cannot just be a win vs. a loss, because a loss could just as easily be due to the improper deployment of the prevent. The prevent is designed to allow short receptions to burn time off the clock, NOT keep the other team from scoring. So if a coach sends out 8 DBs with 2 minutes remaining and the opponent has 3 timeouts, that’s not really a failure of the prevent defense, just like rushing the ball on 3rd and 20 and failing to get the first down is not a deficiency of the tactic of rushing.

My answer to your immediate question is that I don’t know - I’ve never seen any hard analysis of this precise question. What follows is all my opinion.

The principal difficulty here is that the maxim, as so many are, is glib and sort of meaningless. How late in the quarter are we talking, and how soft does the defense have to be to qualify as a prevent? Analyzing NFL trends like this is very difficult because the playbooks are so complex and it’s impossible to tell, really, on any given play whether something happened by design, by blown individual responsibility, or just because the offense beat the defense or vice versa. I’m an Eagles fan, and I can guarantee that Asante Samuel’s location on the field at any given time is far more a product of his own particular mentality than the scheme (since no other Eagles cornerback has ever been instructed to peel off the guy he’s covering and dart underneath receivers running middle routes and get whipped on double moves two or three times a game), so that sort of thing is difficult to be sure about.

For instance, let’s say we go through every NFL game of the last 10 seasons looking for instances of the prevent and checking off boxes for success and failure. How will we know for certain whether a team is playing normal defense or a prevent? It’s one of those things where I’ll know it when I see it, of course, because we’ve all seen the extreme scenario of a two man rush, deep quarters defense where the safety starts 40 yards off the line. But there’s a continuum there from a stacked goal line formation all the way to that anti-Hail Mary defense that’s hard to draw lines on. What about like a normal cover-4 with no blitzing? Is that reasonable defense or chickenshit defense? Certainly you’d see it sometimes in non-endgame scenarios but it’s definitely designed to keep the play in front of the defense, so what do we do with that?

I think unfortunately the answer to the question, much like the controversy over going for that 4th down, is simply that the prevent plays certain odds, and it’s up to the coaches to make sure that the odds they’re playing really represent what they want out of the situation. 3 seconds left, ball on the offense’s 20? Probably most effective to play it safe. Ball on the 50 with six minutes left? The prevent’s probably not going to be your best bet there. Anything in between depends on context, I think, and it’s going to be a judgment call what factors are the critical ones in that analysis. I’d say the prevent doesn’t prevent winning, but shitty coaching sure does.

(that was a very long-winded way to say almost exactly what ReticulatingSplines said a long time ago, as it turns out)

I’m also curious as to what exactly a “prevent defense” is, and what the standards are for defensive effectiveness when trying to win when the trailing team has the ball close and late in the game. Say it’s 2 minutes to go and 80 yards to tie it with a TD. No sane defensive coordinator would put half his secondary 30 yards back-that’s reserved for desperation heaves when just a few seconds and tens of yards lie between the offense and the goal line. Instead if you’ll notice they’ll usually play their nickel package-dime maybe: 5-6 DBs, 1-3 LBs, 3-4 linemen rushing. Yes, one safety will be deep, probably two (cover two), but they usually are anyway in many normal downs throughout most of the game.

Second, the offense knows it has to score, or die trying-they know, in other words, precisely what they need to do to get it done, and how much time they have to do it-fullback plunges up the middle won’t cut it. So yes, in those situations the offense will score more often than they will (% of possessions) in a less nailbiting situation-this is hardly susprising (they’ll also tend to turn it over more often too since they’ll be throwing more high risk passes into coverages loaded with DBs). The defense knows what it has to do-let the offense catch short balls in the middle of the field (and, in college FB, short of the first down)-if they don’t have any timeouts the clock will eventually run out before they get to the goal line.

I see that Jimmy C. pretty much covered all of the above in his post, so I’ll shut up now. IIRC for a few years back in the late 70’s/early 80’s (specifically, after the Staubach-Pearson “Hail Mary” in a 1975 playoff game where the Vikings D was playing a bit too up front), teams went too far to the other extreme, made the coverages too soft, and the other team scored using enough short-to-medium passes to get the job done. More recently the coverages have tightened up again unless like I said it’s really late and long to go.

The NFL network recently did a Top 10 show on the Top 10 Football Myths. #1 was “The Prevent Defense Prevents Winning”.

People remember when it fails, they don’t remember all the times it works.