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NFL & College Football Betting Guide: Understanding Defensive Stats

Few sports are more fun to bet on than football. But even if you have an encyclopedic knowledge of NFL and college football stats, it’s important to know which numbers matter more than others. In this NFL and college football sports betting and strategy guide, I’ll lay out the best numbers to use when evaluating defenses. If you don’t want to do the dirty work yourself, subscribe to OddsShopper Insider Access and check out my NFL betting model. Let’s dig in!

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NFL & College Football Betting & Strategy Guide: Key Defensive Stats

NFL & College Football Betting & Strategy Guide Part 5. Defense

In our first edition, I wrote that football is fundamentally a passing game. Just as the best way to increase your odds of winning when you have the ball is to pass, the best way to increase your odds of winning when you don’t have the ball is to stop the pass. Rushing defenses are nice to have, but they aren’t essential to winning in either the NFL or college football.

For an illustration, let’s look at some numbers from 2022. In the NFL, the season leaders in yards allowed per rush attempt, the Tennessee Titans, failed to make the playoffs. The 32nd and 31st-ranked teams both did. Likewise, two of the three best Power 5 teams by rushing defense, Iowa and Wisconsin, went a combined 15-11.

When evaluating a passing defense, there are two key parts of the game to consider: pass rush and coverage. An elite pass rush can make up for shoddy coverage by pressuring the quarterback, while an elite secondary can make up for a pass rush that struggles to get to the quarterback. Good teams usually excel at either rushing the passer or covering the receivers, but great teams are good at both.

Again, as I said in our first edition, you should care more about yards than points or giveaways. A defense that lets opponents drive downfield but miraculously forces turnovers in the red zone is lucky; a defense that doesn’t let its opponents get into the red zone at all is good. Likewise, points for and points against metrics usually count special teams and defensive scores, which punish defenses for the failures of other personnel groupings.

Evaluating Passing Defense | Football Betting & Strategy Guide

Passing defense obviously comes down to the pass rush and the secondary. It’s almost impossible to evaluate one without the other, so you shouldn’t try very hard to do so. Coverage is inherently baked into stats like pressure percentage, adjusted sack rate and expected points added (EPA) per play — you can’t remove the contributions of the secondary from those numbers. Likewise, the pass rush is inherently baked into stats like yards allowed per pass attempt (YA/PA).

While a few metrics can help us parse out which unit works more effectively, don’t get lost in the weeds too much. PFF grades are useful, especially when trying to quantify the impact of an injured player’s absence. A team with a lockdown corner will obviously have more success rushing the passer if the first option is always smothered. Pass rush win rate also helps because it’s tied to a time interval — 2.5 seconds — by which point a quarterback may or may not have thrown the ball.

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Bettors should also know how to parse out efficient defenses from aggressive ones. If a team with a high pressure percentage also has a high blitz rate, it’s not gaining as much of an advantage as a team with a high pressure percentage and low blitz rate. In 2022, of the top-six teams in pressure percentage, four blitzed less often than they generated pressure. Three of them made it to the playoffs. Two of them made it to the Super Bowl. The two teams with blitz rates greater than or equal to their pressure percentage were quickly dispatched in the postseason.

Unfortunately, the statistical landscape is much different for those looking to handicap college football. Tracking sack yardage as lost rushing yardage makes identifying the best passing defenses difficult. To compensate, standard- and passing-down sack rate numbers are useful, but havoc rate is the most useful. To calculate havoc rate, add a defense’s total tackles for loss (including sacks), pass breakups, interceptions and forced fumbles and divide it by total plays. While that number does bake in some rushing stats, it paints a more accurate picture than the alternatives.

Evaluating Rushing Defense | Football Betting & Strategy Guide

Rushing defense may not matter as much as passing defense, but it certainly matters. Of the three teams to allow fewer than four yards per rush attempt, two made it to the postseason, and one made it to a conference championship. Unlike passing defenses, rushing defenses are much easier to evaluate since the goal is to stop one player — either the running back or quarterback — and not both the quarterback and his intended target. Stats like yards allowed per rush attempt (YA/RA) carry more weight than their per-pass counterparts.

Several advanced stats can help you identify effective rushing defenses. Line yards and stuffed rate reveal how much room a defense affords to the running back and how often the unit manages to stop them behind the line. Run stop win rate reveals how often a team’s run-stoppers break through an opposing offensive line. And, of course, PFF grades can help you determine both how much a player contributes in the trenches and whether their contributions primarily come against the pass or against the run. Do note that an individual player’s tackles and tackles for loss matter less than you’d think; a nose tackle who occupies two offensive linemen and allows a replacement-level linebacker to get the tackles is obviously more valuable than the player receiving the counting stats.

Rushing quarterbacks are a complication for evaluating a rushing defense. Unlike a traditional rushing play, quarterback scrambles force a defense to shift from playing against the pass to playing against the run, which can often expose units that are otherwise good at stuffing the run. The 2022 Miami Dolphins were a good example of this phenomenon: they ranked fourth in adjusted line yards, sixth in stuffed rate and eighth in run-stop win rate but gave up the second-most rushing yards to quarterbacks, dropping the team to eighth in YA/RA. However, the Dolphins allowed the third-fewest rushing yards to running backs.

Again, the limitations of college football stats make evaluating a collegiate rushing defense more difficult than evaluating a professional one. A top-tier team in YA/RA may actually just have a good pass rush and a slightly above-average rushing defense. Fortunately, line yards can help us parse that out — San Jose State, which ranked eighth in yards allowed per rush attempt (3.3) ranked only 48th in line yards (2.56), largely as a function of pass rush, which ranked second in sacks per game (3.6). When faced with a run-heavy Utah State attack late in the year, the Spartans coughed up 125 yards and three touchdowns to running back Calvin Tyler Jr.

Evaluating the Defense as a Whole | Football Betting & Strategy Guide

My favorite metric for evaluating a defense as a whole is expected points added (EPA) per play, which you can also split up by dropback and rushing attempt to evaluate the performance of more specific units. In 2022, three of the top-four teams in defensive EPA per play made the playoffs, with two making it to the conference championship round and one going to the Super Bowl. Although a good defense can’t fix a bad offense, it certainly can help.

But because EPA metrics aren’t readily accessible for college football bettors, leaning on yards allowed per play (YA/P) and havoc rate are good all-around tools to have. The former stat tells you what a given defense is giving to its opponents; the latter stat tells you what that defense is creating for itself. Nine of the top-10 teams by YA/P went to a bowl (the lone exception, James Madison, was postseason ineligible) while just one of the bottom-10 teams did.

Index

Part 1. NFL & College Football Betting & Strategy Guide: Offense
Part 2. Expected Points Added (EPA)
Part 3. Net Yards Per Attempt (NY/A)
Part 4. Passing Efficiency
Part 5. NFL & College Football Betting & Strategy Guide: Defense 

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