How Is Iowa's Defense So Good This Year?

By RossWB on November 7, 2019 at 11:00 am
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© Matt Marton-USA TODAY Sports
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There's one reason that Iowa enters November at 6-2 and with a shot at claiming a Big Ten West title this season and it's the same reason as almost every year that they've been a contender in the Big Ten under Kirk Ferentz: it's the defense, stupid. Phil Parker has once again engineered a stout defense that's put the clamps on opponent after opponent and given Iowa chances to win every game this season. The players change, but the results don't for the Iowa defense.

This year's defense has already posted two shutouts. Only one team has even cracked 20 points against them -- Purdue, who scored precisely 20. Six of Iowa's eight opponents posted season lows in points in their games against the Hawkeyes. Iowa ranks third in the nation in scoring defense (10.1 ppg), eighth in the nation in total defense (265.9 ypg), eighth in the nation in defensive efficiency (per SP+), and eleventh in the nation in yards per play (4.46 ypp). 

So how are they doing it? 

1. They're keeping the defense off the field as much as possible.

Iowa's defense has faced 477 plays this year, their third-lowest total in the nation (fun fact: Wisconsin's defense has faced the second-fewest plays, 468). Iowa's offense hasn't actually run that many plays -- 573, which ranks 81st in the nation. But the offense takes its time when it's on the field; Iowa ranks seventh nationally in time of possession, at around 34 minutes and 21 seconds a game. (Wisconsin leads the nation in T.O.P., with 36:48, while Minnesota is sixth, with 34:43.) Time of possession doesn't inherently say much about the quality of an offense, but in this case it's a boon for Iowa's defense; it's a lot harder for the other team to score if they don't have the ball. 

2. Iowa's defense has been very good at getting stops.

They rank 5th in FBS with an 83.9% stop rate ($). Stop rate is the percentage of a defense's drives that end in punts, turnovers, or turnovers on downs. So opponents are scoring points on Iowa less than two out of every ten times they take the field on offense. That's very very good! Incidentally, the Big Ten is ridiculous this season when it comes to stop rate. Four of the top five teams nationally in stop rate are from the Big Ten: #1 Ohio State, #2 Penn State, #4 Wisconsin, and #5 Iowa.  

3. Iowa's defense has been excellent at forcing three-and-outs.

This is probably what you'd expect given the stop rate stat. Iowa ranks 12th nationally ($) in forcing three-and-outs, with 41.9%. So about four out of ten times the opposing offense takes the field, they go three-and-out against Iowa's defense. Interestingly, Iowa is just 26th nationally in opponent third down conversion rates; opponents are converting third down about 33% of the time. 

4. Iowa has been outstanding at limiting big plays for the most part.

They haven't allowed a single rush of 20+ yards this season. They lead the nation in fewest plays of 10+ yards allowed, with 65 (Ohio State is #2 there, with 70). They're second in the nation in fewest plays of 20+ yards allowed, with 17 (Utah is best, with just 15 such plays allowed). They're also second in fewest plays of 30+ yards allowed (6) and 15th in fewest plays of 40+ yards allowed (5). We remember the few breakdowns that have occurred -- the bombs that Iowa State hit against Iowa or the long pass to David Bell during Purdue's teased comeback -- but that's mainly because of how rare they've been. Iowa's defense has done a tremendous job of eliminating big plays and forced offenses to methodically grind out drives, which has proven very difficult. 

5. Iowa has kept teams out of the red zone.

Opponents have made just 13 trips inside the Iowa 20-yard line, tied (with Georgia) for the fewest such trips in the nation. The defense hasn't quite been nails inside the red zone -- teams have scored on 11 of those 13 trips (84.62%), with six of them being touchdowns (46.2%) -- but teams simply haven't been able to get many opportunities in the red zone against Iowa. This ties into the first point, about keeping the defense off the field; the fewer plays Iowa's defense is out there, the fewer chances an opponent has to get into the red zone. That is, assuming that defense is also preventing big plays -- which we know the Iowa defense is. Teams haven't had much success connecting on big hitters against Iowa and they haven't had much luck grinding out long drives, either. 

So that's a lot of good news about Iowa's defense. But is there cause for concern? Maybe.

1. Iowa has been poor at sacking the quarterback.

They have just 16 sacks, which puts them 83rd nationally. There are ways to pressure the quarterback without necessarily getting a sack and Iowa has been able to do that pretty well -- but the low sack total is still concerning. Iowa has also been pretty lousy at producing tackles for loss this year; they have just 35 tackles for loss this year, which puts them in a tie for 122nd (with Army, Georgia State, and Rutgers) nationally. 

That said, part of the reason for those numbers is Iowa's defensive philosophy. Iowa's defense is not, as a general rule, super-aggressive, particularly when it comes to blitzing. They're generally content to give up two, three, four yards and keep the opponent in front of them rather than gambling for a bigger stop -- and potentially letting the opponent get behind them for a big play. Iowa is never among the national leaders in sacks, although they've been better than this in recent years (national rank the last four seasons: 25th, 45th, 54th, 42nd). Likewise, they often rank fairly low in terms of tackles for loss (national rank the last four seasons: 75th, 96th, 110th, 106th). But how low is too low? Iowa's defense can be successful without a ton of sacks or tackles for loss... but they generally need some of those stats and they're getting very few of them this year. 

2. Turnovers are another area of concern with this Iowa defense.

One of the reasons Iowa has had so much success on defense in recent years is because of their ability to generate turnovers. They were 8th last year with 27 turnovers (including 20 interceptions, 3rd most nationally). They were 16th in turnovers in 2017 with 26 (including 21 interceptions, most nationally). They were just 78th in turnovers in 2016 with 18 (including 9 interceptions). And in 2015 they were 14th in turnovers with 27 (including 19 interceptions, 10th best nationally). This year Iowa has forced just 10 turnovers, which ranks 96th nationally, and just six interceptions (76th nationally).

Takeaways obviously help Iowa's defense (by getting them off the field) and also Iowa's offense (by usually giving them a shorter field to work with); not generating many turnovers this year has made it tougher on Iowa's offense (they have to drive longer to score points, which is not ideal for this attack) and puts a lot of strain on the defense. Obviously it hasn't been a big problem for Iowa's defense thus far... but can they maintain this high-wire act through the rest of the regular season? 

3. The opposing offenses are going to get better

Because that's the final area of concern: the quality of the opposing offenses is set to increase (for the most part). Here are some of the offensive ranks of Iowa's first eight opponents: 

OPPONENT TOTAL OFF SCORE OFF OFF EFF
Miami (OH) 123 (294.4 ypg) 105 (22.7 ppg) 113 (29.2)
Rutgers 126 (280.3 ypg) 127 (14.7 ppg) 122 (16.9)
Iowa State 16 (479.5 ypg) 25 (35.9 ppg) 32 (66.3)
Middle Tenn St 76 (398.3 ypg) 90 (24.9 ppg) 83 (43.9)
Michigan 82 (389.9 ypg) 51 (31.8 ppg) 40 (76.2)
Penn St 52 (422.1 ypg) 12 (38.5 ppg) 6 (84.8)
Purdue 89 (387.7 ypg) 95 (24.6 ppg) 84 (43.8)
Northwestern 128 (258.0 ypg) 130 (9.8 ppg) 119 (17.9)

Miami (OH), Rutgers, and Northwestern have three of the worst offenses in all of FBS this year. Middle Tennessee State and Purdue have subpar offenses as well. Iowa's defense smothered them all (save Purdue)... but the degree of difficulty wasn't exactly through the roof. Iowa has faced some better offenses -- Iowa State and Michigan rank in the top-third of FBS and Penn State ranks around the Top 10 in scoring and offensive efficiency -- and they had success against them as well (Iowa went just 1-2 against those opponents, but the defense certainly did its part to give Iowa a shot to beat Michigan and Penn State). So that's encouraging. 

And here are the ranks for Iowa's next four opponents: 

OPPONENT TOTAL OFF SCORE OFF OFF EFF
Wisconsin 62 (412.1 ypg) 27 (35.6 ppg) 13 (76.9)
Minnesota 47 (429.5 ypg) 14 (38.4 ppg) 15 (75.0)
Illinois 114 (325.8 ypg) 60 (30.0 ppg) 114 (28.7)
Nebraska 65 (409.1 ypg) 82 (26.3 ppg) 73 (47.1)

The real test is in Iowa's next two opponents. Illinois is generally fairly lousy on offense this year but has been able to score a good amount of points, thanks in part to a +12 turnover margin and five defensive touchdowns. Nebraska's offense isn't particularly great, but they do rank higher in offensive efficiency than five of Iowa's first eight opponents. But Wisconsin and Minnesota are each in the Top 30 in scoring offense and the Top 15 in offensive efficiency. Much has been made of Minnesota's schedule and it's certainly been weak so far -- but in Big Ten play they've absolutely been creaming those weaker opponents.

Again, Iowa's defense has done well against good offenses this season -- see: Iowa State, Michigan, Penn State -- and they're going to need to be again for Iowa to have a shot at winning in November. If they can maintain the same success they've had at getting opponents off the field quickly, forcing three-and-outs, preventing big plays, and keeping opponents out of the red zone, they'll be in great shape. If they can work in a few more sacks (and tackles for loss) and force a few more turnovers, it will probably make the defense's job even easier. Given the struggles of Iowa's offense this year, the Hawkeyes are going to need to rely heavily on the defense to have a successful November. They've been up to the task so far this year -- let's hope they can keep it going for a few more weeks. In Phil We Trust. 

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