Tag Archives: Football Outsiders

How Good is Denver’s Defense?

The Broncos’ defense is incredible. It’s otherworldly. It’s unstoppable.

While those three superlatives are perfectly reasonable things to say, they don’t say why the Broncos’ defense is so good. Instead of continuing on with opinion and conjecture, let’s take a look at a few statistics to determine just how good Denver’s defense is.

Simple measures of defensive performance are useful but limited. For instance, the Broncos allowed 18.5 points per game this season, an elite rate. However, that only ranks fourth in the NFL, behind Seattle, Cincinnati, and Kansas City. Clearly, this statistic is unable to show how great Denver’s defense is.

Instead, let’s use DVOA (check out this article for an in-depth explanation of DVOA). The Broncos’ defensive DVOA is an impressive -25.8% (remember that positive numbers represent more points so a negative DVOA is good for defenses). How good is that? First let’s take a look at a graph.

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This graph shows the distribution of defensive DVOA in the NFL in the 2015 season. Thirty of the thirty-two teams in the NFL are in the same cluster in the middle. The square in the upper right corner is the laughably bad Saints defense. The star all the way in the bottom left corner? That’s the Broncos.

Just look at the gap between them and second place. Although it’s not quite as large as the one between New Orleans and 31st-ranked Chicago, it’s still a fairly sizable gap. That’s how much better Denver’s defense is than everyone else’s.

Here’s another way to measure how dominant Denver’s defense has been: z-score. If you’re unfamiliar with the term, z-score measures how many standard deviations a given data point is over or under the average of all the data points in the sample.

Denver’s z-score is -2.31. As a comparison, here are eight other notable defenses in recent years and their z-scores based on defensive DVOA. Remember, a negative z-score is good for defenses, as it means that they are successful at preventing points (or producing negative points, if you will).

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As you can tell, this year’s Broncos defense stacks up very well against some of the best defenses in recent memory. A couple of non-Broncos notes:

  1. The Buccaneers were crazy-good back in 2002. Given a normal distribution, the chances of a defense being better than Tampa Bay’s in 2002 are just over .01%. Wow.
  2. To many, the 2000 Ravens own the title of best defense of the 21st century. However, on this list, they rank last. Why is that? Well, if you look one slot above them, you’ll find the 2000 Titans, who (obviously) played in the same season as them. Standard deviation, and, as a result, z-score, can be affected by the presence of a team of a similar caliber. Accordingly, the Ravens’ z-score is dragged down by the presence of the Titans.

There’s one more way to show how great Denver’s defense is this season. Given a normal distribution, the chances of a defense being better than the Broncos’ defense are 1%. That means that you’d expect a defense as great as the Broncos’ to show up roughly once every 3.125 seasons. So, with these Broncos, you’re seeing something that only occurs about three times a decade.

Although we’ve answered the titular question pretty thoroughly, there remains one, far more important question that has yet to be answered: Will this spectacular defense result in a championship?

Not having a star quarterback is a significant roadblock to winning the Lombardi Trophy, but not an insurmountable one. In recent years, pedestrian quarterbacks such as Joe Flacco, Brad Johnson, and Trent Dilfer have won Super Bowls. Flacco was helped along by an extraordinary hot streak, but both Johnson and Dilfer were accompanied by excellent defenses, both of which appear in the chart above.

Now, since we’ve already established that Denver’s defense is superb, it would stand to reason that they would have a genuine shot at the championship despite their lackluster quarterback situation. That’d be true if it were Brock Osweiler who were starting for the Broncos at quarterback in the playoffs as he’s been competent enough to allow them to win games. However, rather than Osweiler, it’ll be Peyton Manning starting under center for Denver. Manning, unlike Osweiler, has proven himself to be totally incompetent this season, throwing an interception of 5.1% of his attempts, an absurd rate.

While great defenses can carry mediocre signal callers to Super Bowl victories, even the best defenses can’t overcome abysmal quarterbacking. And, even if Manning were playing like he was in 2006, I certainly wouldn’t want to entrust my Super Bowl hopes to a guy who looks like he’s plotting to murder John Elway.

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DVOA FAQ

What is DVOA?

DVOA is a statistic created by Football Outsiders and stands for Defense-adjusted Value Over Average. Translation: DVOA shows how good (or bad) you are compared to an average team. DVOA is a percentage, with a league-average DVOA being 0%.

How is DVOA calculated? 

Put simply, DVOA is calculated by comparing every single play in the season to a league average baseline. It’s then adjusted for strength of opponent, game situation, and field position. Additionally, DVOA values successful plays more than other plays. A successful play is considered to be a play that gains 45% of the yards needed for a first down on first down, 60% of the yards needed on second down, and 100% of the yards needed on third and fourth downs. In other words, if you gain eleven yards on a 3rd-and-16, it matters a lot less than gaining six yards on a 3rd-and-4. DVOA is able to take this difference into account, unlike simpler statistics.

How can I interpret DVOA?

On offense, a positive DVOA means that you’re better than average while on defense, a better than average team has a negative DVOA.

What’s the reason for this discrepancy?

DVOA is a measure of how many more points you create than an average team. On offense, the best teams create more points than an average team, so their DVOA is positive. However, on defense, the best teams prevent more points than an average team, so their DVOA is negative, because they create “negative points”.

Why is DVOA better than simpler statistics like points scored and allowed?

DVOA is better than simple points scored and allowed because of its increased accuracy and predictive value.

How does DVOA gain its accuracy?

As mentioned before, DVOA is adjusted for a number of factors. In addition to the three mentioned above, DVOA is based on plays, rather than points. This is important in a couple of ways.

One, if the offense throws a pick-six, that shows up as points allowed for the defense. However, it was obviously the offense’s fault, not the defense’s. Simple statistics attribute those points to the defense, but more advanced metrics like DVOA correctly assign blame to the offense.

Two, while points allowed only records drives that end in scores, DVOA takes note of every play on every drive. For instance, let’s say that Team A gives up fourteen points and 250 yards per game, while Team B gives up fourteen points and 350 yards per game. By simple measures such as points allowed, Team A and Team B have equal defenses. However, by DVOA, it’s clear that Team’s defense is better than Team B’s on a play-by-play basis.

Are there any other details I should know?

There’s one important factor we’ve only mentioned so far, and that’s DVOA’s adjustment for field position. If your quarterback throws an interception and your opponent starts their position on your one yard-line, then it’s very likely, even if your defense is spectacular, that you’ll give up a touchdown. The opposite is true as well. DVOA gives your offense more credit for long drives than for possessions that begin in your opponent’s red zone.

Simple statistics don’t measure that. To them, a one yard drive for a touchdown is equal to a methodical fourteen play, ninety-two yard drive for a score.

There are various other permutations of DVOA that we won’t discuss in this particular article. One notable one, however, is DYAR, which is DVOA but in a cumulative statistic, rather than a rate one.

In future football articles, we’ll be using DVOA a lot more, and I hope you find this FAQ useful so you’ll be able to be a more discerning football fan. And, even if you still don’t understand it, it’s a fancy sounding statistic with an acronym; just using it in a sentence makes you sound about three times as smart.

Should the Giants Sit Their Stars?

The Giants are finally nearing the end of yet another lost season. Only one more game remains: a matchup against the Eagles at 1:00 this Sunday.

While they get all the attention, teams that are locked into their playoff seeds aren’t the only teams who have to think about benching their stars. This week, the Giants face an intriguing decision: should they sit their studs to keep them safe or should they play them for pride?

The main reason the Giants should consider sitting players like Eli Manning and Odell Beckham Jr. is that it makes no sense to risk your star players over a meaningless regular season game. Football is an inherently dangerous sport, and the more one plays it, the more likely it is that one gets hurt.

Those who think that teams should play their stars, even in meaningless games, like to point out that Week 17 is no more dangerous to players than any other game, as shown in the graph below.

In this graph, (found here, at Football Outsiders) the orange line shows that the risk of sustaining a new injury is stable throughout the season (Week 1 looks like a significant outlier, but, as the article notes, “anybody who suffers an injury in the offseason, training camp, or preseason will first appear” in Week 1’s stats). Accordingly, the logic goes, teams should play their stars because the risk of sustaining a new injury in Week 17 is no greater than the risk in any other game.

There’s an easy retort to this argument. While it’s true that a player is not more likely to get injured in Week 17 than in any other week, it’s also true that a player is more likely to get injured playing in a Week 17 game than sitting it out. Why should the Giants increase the risk of an injury to Manning or Beckham Jr. even slightly by playing them in a meaningless game?

It’s important to note that this graph does not indicate what kind of injuries were sustained. Obviously, there’s a significant difference in importance between a mild hamstring strain and a torn ACL, and that difference needs to be taken into account when determining the risks of playing one’s stars in a meaningless game. Logically, there’s no reason why the rate of serious injuries in Week 17 should be different than in any other game, but if anyone has any statistics on the matter, please email me at sushionsports@gmail.com.

Many will say that Eli Manning’s streak of 150 consecutive games started should not be broken, and that he needs to play to keep the streak alive. However, there’s a simple solution to this problem: play Manning for the first series of the game, and then sit him down for the rest of the afternoon.

The biggest reason the Giants should play their stars is out of loyalty to their fans. This game is being played in the Meadowlands, the Giants’ home stadium. The cheapest seat in the stadium, according to StubHub, is $50. That’s a significant amount of money to shell out for a team that’s not trying to win.

The Sixers, the preeminent tanking team, have realized that no one wants to pay a lot of money for a team that intends to lose. Accordingly, for their next home game, against the Timberwolves, the cheapest ticket available on StubHub is for a grand total of $9. That’s all. The price for a seat right behind the basket is $44. That’s cheaper than the cheapest seat in MetLife Stadium!

The Giants owe it to their fans, who are paying a lot of money to come watch the team play, to do their best to win the game. If it was on the road, that’d be another story, but it’s not. People come to Giants games to see Beckham Jr. and Manning, not Sidney York and Ryan Nassib.

And, just to prove my point, you definitely didn’t realize that Sidney York is the name of an electro-pop band, not a football player. Rather, it’s Elliott Brood who’s the current WR6 on the Giants.

So what do I think the Giants should do? It’s a tough decision, and I’m glad I don’t have to make it. Still, if I had to choose, I’d lean towards playing the stars for the sake of the fans. If I’m the Giants, I definitely don’t want to be compared to the Sixers.

And besides, who wants to see guys like Elliott Brood play football? Well, actually, it might be pretty awesome as, although you didn’t notice, Elliott Brood isn’t a wide receiver; it’s a Canadian alt-country band. And unless you want to see these guys playing for the Giants, you’d better hope the starters are playing on Sunday.

This article can also be found at Jock Journal.