2018 Virginia Football Previews: What are these numbers and what do they mean?

If there’s any fanbase in the country that understands the importance of looking at stats that account for pace and possessions, it’s fans of the Virginia Cavaliers.

With UVA basketball under Tony Bennett consistently ranking among the nation’s slowest teams—measured by possessions per game—its fans have learned to embrace not just the pace, but pace-adjusted metrics of basketball success. Efficiency gurus like Ken Pomeroy and Bart Torvik have elevated those numbers into prominence in the national hoops dialogue, and they’ve become a big part of how we cover the Hoos here on Streaking the Lawn.

This year, we’re going to do the same for our football coverage.

Once you start looking at numbers underneath just wins and losses, the baseline for any statistical analysis in sports boils down to the same premise: measuring the frequency and magnitude of success. When you have the ball, how often did you score, and how much did you score when you did? When the other team has it, how often did you let them score, and how much did they score when they did? That’s all of it, in two deceptively simple questions.

Where it gets tricky—and fun—is accounting for the different ways to reach the same metric of success. In basketball, say the “ideal” offensive metric is 1.0 points per possession. At the extremes, assuming no turnovers and no rebounds, one team could accomplish that by only shooting three-pointers and scoring on 33% of its possessions, while another could take only two-point shots and score on 50% of its possessions. Each approach creates the same outcome, but they vary wildly in which other correlated factors will become important.

Football gets the added level of complexity brought about by field position. A drive that starts at your own 10 is far less of a scoring opportunity than one that starts at your opponent’s ten. “Success” in the former instance might mean getting the ball to the 40 and then punting; in the latter, you gotta get some sort of points, and there’s a solid argument that even scoring a field goal would not be a successful drive.

The tool we’ll be using to interpret that dizzying mass of complexity is Bill Connelly’s S&P+ metric, along with its component pieces.

Connelly’s site for advanced stats here on the SB Nation platform—Football Study Hall—should go in your bookmarks right now. We’re using this article to introduce some of the basics underlying the stats we’ll integrate into our football coverage this year. But the articles and definitions on FSH will completely change the way you watch, analyze, and understand the game. Trust us on this.

At its core, S&P+ measures two things: the rate of Successful plays (the “S”), and the Points scored per successful play (the “P”).

Defining success

So what counts as a “successful play?” Here’s Bill:

The goal of success rate is to create an on-base percentage-style efficiency measure. Depending on a given down and distance, each play is deemed successful or non-successful:

First downs: gaining at least 50 percent of necessary yardage (usually 5 yards) is successful.

Second downs: gaining at least 70 percent of necessary yardage is successful.

Third or fourth downs: gaining at least 100 percent of necessary yardage is successful.

That’s it. And it matches up perfectly with many of the concepts we already use to describe successful offense, like moving the chains, staying ahead of schedule, or throwing beyond the sticks. The formula for success rate quantifies what we already know: a two-yard run on first down is going to hurt you, and a five-yard pass on third-and-eight does you very little good.

Points: turns out they’re good

OK so you had a successful play. But what did it get you? What was the magnitude of success associated with the frequency of it?

The component of S&P+ that measures explosiveness is IsoPPP+: isolated points per play, adjusted for opponents (which is what the “+” always means). Getting to the unadjusted number is easy, at least in terms of the arithmetic. Take the number of points, divide it by the number of successful plays, and voila, you’ve got IsoPPP.

Just like success rate, IsoPPP lines up a quantitative measure with our qualitative understanding. Most football fans expect big plays more from the passing game than on the ground. In 2017, the national average IsoPPP on passing plays was 1.48; for rushing, it was only 0.92. Which is to say that you would expect half a point more per successful passing play than you would for each successful running play.

Reading the numbers

Putting success rate and explosiveness together with the other three “Five Factors”—field position, finishing drives, and turnovers, each of which has its own measurement—gets you to a final S&P+ number for each team. On Football Outsiders, the number is presented as “S&P+ Margin:” how many points per game better or worse each team is than the average college football team that year. Again, Bill’s illustration:

For instance, if Team A’s S&P+ rating is plus-19.0, that means it is 19 points better than the average college football team. If Team B’s rating is minus-12.0, it is 12 points worse than average. And if Team A and B were playing on a neutral field, you could determine that S&P+ would favor Team A by 31 points (19 minus minus-12).

Let’s put some of these concepts into practice, looking at UVA’s 2017 advanced stats profile.

When UVA ran the ball, they achieved a “successful” result 37.5% of the time—four and a half percentage points below the national average. And when they were successful, they scored at only 81 percent of the national average. Just by looking at these numbers, even if you hadn’t watched a single down of Virginia football with your own two eyes, you could tell that the rushing game was anemic, with lots of plays that went for very short yardage and very few big plays.

On defense, these metrics tell us that UVA did a somewhat decent job—basically right at the national average—when it came to stopping run plays short of what they needed. But when running plays did break through, they tended to go for big yards.

Now, to the air.

So the passing game for UVA was still below the national average in terms of success rate, but not AS far below as the run game was. The super low IsoPPP tells you that Virginia was a team that used the passing game as its main option for advancing the ball down the field. For every 60-yard bomb to Andre Levrone (high IsoPPP), there were several swing passes and short dump-offs to Olamide Zaccheaus (high success rate, low IsoPPP)—and plenty of drops (tanking the success rate).

The pass defense was something close to elite, at least for a sub-.500 team. A success rate that’s four points below the national average and a better-than-average IsoPPP means receivers were well covered and tacklers were quick to the ball. This is what you would expect from a defense with an All-American safety and a senior leader at linebacker keeping the alignments correct.

That’s a very quick and dirty rundown of some of the concepts you’ll see here on STL as we work to improve how we cover an improving football program. A full glossary of other advanced stats—like how to account for field position, or what a Havoc rate is—can be found at this link.