CHAPEL HILL, N.C. – For all of the fanfare surrounding Gene Chizik, his 4-3 scheme and his change in philosophy, the defense’s improvement in 2015 will be measured by one statistic: scoring defense.
The Tar Heels set ACC single-season records for most points allowed (507) and most touchdowns allowed (67) in 2014. UNC allowed 39.8 points per game against FBS opponents and 46.6 points per game in its seven losses.
Those types of statistics tend to simplify how Larry Fedora will measure improvement under his new defensive staff. The fourth-year UNC head coach is cemented in his long held opinion that his defense needs to hold its opponent to one less point than his offense scores.
When asked to expand beyond those parameters in defining defensive improvement last week with such metrics as tackles for loss, third-down percentage defense and other defensive buzz words, Fedora once again emphasized the scoreboard.
“It still comes down to scoring,” Fedora said. “That’s the key to the whole thing. Obviously, we’ve got to be much better than we were in that avenue or we won’t have a chance.”
It helps that the Tar Heels held their opponents to 24.5 points per game in 2013, worthy of a top-50 ranking nationally and a sixth-place finish in the ACC. How UNC returns to that level requires a look into how the 2014 season went so wrong.
First, the good news. UNC ranked 23rd nationally in opponents’ starting field position (27.4 yard line) in 2014, according to FootballOutsiders.com. The Tar Heels also ranked 36th in opponents’ short field drives (0.90), which denotes the percentage of drives starting at midfield or on the opponents’ side of the field.
Field position statistics are important due to their correlation with points scored on any given possession. Brian Fremeau of BCFToys.com charted more than 132,000 offensive drives between 2007-2014 and discovered a direct correlation between field position and points scored that confirms the common sense approach that a team scores more points the closer it gets to the end zone.
Given UNC’s opponents’ starting field position at the 27-yard-line last fall, Fremeau’s data indicates those opponents should have scored on 31.6 percent of their drives and scored touchdowns on 23.0 percent of their drives.
In actuality, UNC’s opponents scored on 58.5 percent of their drives and scored touchdowns on 42.6 percent of their drives. That’s how the Tar Heels set a new ACC record with 67 touchdowns allowed in 2014.
Dave Bartoo of CFBMatrix.com provided further insight into UNC’s inability to capitalize on solid defensive field position. According to Bartoo’s data, UNC ranked 16th nationally in opponents’ starting field position (72.9), yet ranked 99th in opponents’ ending field position (33.3).
Key Stats to Watch
In attempting to explain the discrepancy, it makes sense to look at the two primary statistics Larry Fedora dissects when grading his defense – turnovers and explosive plays.
Turnovers, while playing a crucial role in determining wins and losses, are largely random and coaches have little control in winning the turnover margin battle. A study by Ed Feng at ThePowerRank.com found that both fumble rates and interception rates “strongly regress to the mean” over the course of a season.
For example, UNC led the nation in interceptions (14) through the first six games of the 2008 season, but managed just six picks over its final seven games.
Explosive plays, on the other hand, can be designed and executed – or limited, from the defensive perspective - with the right mix of coaching and recruiting. These types of plays explain why the Tar Heels failed to capitalize on its opponents’ field position.
UNC defines an explosive play as a run of at least 12 yards and a pass of at least 16 yards. The Tar Heels manufactured 28 explosive plays while allowing 48 through the first four games of 2014. Taking an even broader look, UNC’s sports information department tracks runs of at least 15 yards and passes of at least 20 yards. The Tar Heels allowed 94 explosive plays using those metrics while creating 69.
UNC’s 2014 opponents tallied 37 plays of 30 yards or longer.
Bill Connelly of www.footballstudyhall.com broke down more than 100,000 plays during the 2013 season and found that a team possessing a 0.5-to-1.0 differential in yards-per-play during any given game won 72 percent of the time. Push the margin to 1.0-to-1.5 and the team won 86.2 percent of the time.
UNC was 4-1 in games in which it won the yards-per-play statistic in 2014, and 2-6 in games it lost that differential. One prominent outlier: Connelly’s data suggests that a team possessing a 2-3 yards-per-play margin wins 95 percent of the time, yet the Tar Heels upset Georgia Tech, 48-43, despite a negative-2.28 yards-per-play differential (8.86-6.58).
Since Fedora arrived prior to the 2012 season, UNC is 14-0 in games in which it has won both the yards-per-play and turnover margin and 0-8 in games in which it lost both metrics.
Two-deep zone coverage schemes – which Butch Davis ran in Chapel Hill and what Chizik will run in his modified Tampa-2 – are often criticized for “bend-but-don’t-break” characteristics, but the reality is that the schemes are designed to limit big plays and force offenses to settle for short gains, thereby requiring lengthy drives to score. The reasoning is that more offensive snaps lead to more opportunities for miscues and turnovers.
Simply by limiting its opponents’ explosive plays, UNC could see dramatic improvement in its scoring defensive this fall.