Northwestern spread offense trends: what the numbers say

"Spread up-tempo."

Whether you hear it from Pat Fitzgerald, offensive coordinator Mick McCall, wide receiver coach Dennis Springer, or former quarterback Trevor Siemian, that seems to be the official classification of Northwestern's offense.

However, last season, on more occasions than one, we challenged that assertion. Was Northwestern really still dedicated to the spread? Or had the Wildcats strayed from what had made their offense so successful in the past in favor of a more power-based scheme?

Here's what our Kevin Trahan wrote following Northwestern's 31-24 loss to Cal in the 2014 season-opener:

"Northwestern is a spread team through and through — the Wildcats are even credited with popularizing the offense. But last year, and in the first game of 2014, NU has been unwilling to fully commit itself to the spread, even though it has all the personnel to be successful.

Too often, the Wildcats abandon the spread and all of its advantages — "spreading the field" and forcing the defense to be responsible for more space, namely — to become a situational power team."

A few days later, I looked at film from the same game to show how Northwestern's "spread" had seemingly regressed, and wrote:

"For years, Northwestern was innovative. The Wildcats were leading the charge for the spread offense, and in the process, beating teams that the talent on their roster suggested they shouldn't. But recently, rather than continue to do so, or even merely adapt with the times and adopt the new wave of the spread, Northwestern has gone in the opposite direction. And in the process, conversely, NU lost to a team Saturday that the talent on its roster suggested it shouldn't have lost to."

All this is to say that there are legitimate questions about Northwestern's and Mick McCall's offensive philosophy. Despite both of those articles coming after just one game, the trend, for the most part, continued throughout the season. There were some notable exceptions — the Notre Dame game comes to mind, but maybe that's just because NU had so much success on offense that day — but generally, the Wildcats seemed to feature more power packages than they had in the past.

But why speculate when we have stats that speak to that very question?

Last year, SB Nation's college football stats guru Bill Connelly introduced an intriguing way to measure how effectively teams spread the field: the percentage of opponent tackles that are solo tackles, as opposed to assisted tackles. The idea is that the more an offense is able to spread the field and get its players in space, the higher an opponent's solo tackle percentage. So as solo tackle percentage goes up, the more an offense spreads the field because the defense is forced to make more solo tackles, which occur most frequently on the fringes of the field, where a spread offense is more likely than a pro-style offense, for example, to operate.

This is clearly and admittedly an imperfect measure. But at the very least — and I'd encourage you to read Connelly's analysis — it is a pretty good indicator of how well an offense is able to get its skill-position players in space — which, in the end, is the goal of the spread offense.

To be clear, this is not a direct measure of how successful a spread offense is in terms of scoring points, but in actually spreading out a defense in terms of distance to bring more one-on-one matchups in open space.

When Connelly first compiled the data last year, the results gave merit to the theory. The top five solo tackle percentage offenses in 2013 were all notable spread offenses: Kansas State, Texas Tech, Arizona State, Baylor and Indiana.

Now, if we've accepted solo tackle percentage as an imperfect but reasonably accurate metric in measuring how well an offense stretches a defense, how does Northwestern stack up?

Here are this year's numbers, courtesy of Connelly:

Northwestern's offensive trends

- 2013: Northwestern ranked 51st (out of 125 teams) nationally in 2013 with a "%Solo" of 75.5 percent.
- National Trend: Overall, from 2013 to 2014, teams became more ‘spread-happy.' The national average for "%Solo" in 2013 was 73.5 percent. In 2014, it rose by 1.2 percentage points to 74.7 percent.
- 2014: Northwestern's "%Solo," however, fell by 1 percentage point to 74.5 percent, which ranked 68th in the country and was below the national average.

This does not mean Northwestern is not a "spread offense." Because of the proliferation of spread offenses, being below the national average doesn't disqualify an offense from being labeled as a "spread offense." And, as mentioned, the stat surely features some degree of error.

But as college football as a whole continues to feature more spread attacks, it seems that Northwestern is, even if only ever so slightly, moving in the opposite direction. And for a team that classifies itself as "spread up-tempo," being below the national average in "%Solo" seems at least somewhat contradictory.

To be fair, Northwestern still plays an up-tempo style, coming in as the 30th-fastest offense in 2014 using Connelly's Adjusted Pace stat — a measure of the number of plays a team runs, accounting for the ratio of run and pass plays. So that part of NU's spread offense still seems to be intact. But spread styles should encompass a focus on both aspects.

It's also important to note that spread offense doesn't necessarily equal efficient offense. There seems to be a slightly positive relationship between the two, but there are plenty of offenses toward the bottom half of the solo tackle percentage list that are highly successful.

However, as both Kevin and I wrote last year, Northwestern's offensive identity has always been the spread. And while the idea that NU has moved away from it might still be up for debate, the idea that the Wildcats have take a step back offensively is indisputable:

(data from Football Outsiders)

If Northwestern is in fact intentionally deviating from the spread, perhaps there's a period of transition to adapt to new schemes and new philosophies that helps to explain why this deviation corresponds with the dip in efficiency. And of course, personnel plays a role too, and Northwestern had serious issues both on the offensive line and at receiver in 2014.

However, Northwestern's recruiting has improved significantly in recent years, and recruiting rankings are a good predictor of a player's talent, so it'd be foolish to suggest NU's personnel has fallen off. Perhaps some of that talent is still developing and is ready to break out this year, or instead, perhaps that talent is being misused in an offense that doesn't cater to its strengths.

Whatever the explanation, it does in fact seems like Northwestern has, to some extent, gotten away from the spread principles that in the past allowed its offense to be potent, and over the past four years, that trend has coincided with a marked decline in offensive efficiency.