Thursday, May 02, 2019

2018 Yards Per Play: Pac-12

After nearly two months of G5 posts interspersed with some basketball musings, we return to the Power Five. At least in name. This week we examine the Pac-12.

Here are the Pac-12 standings.
So we know what each team achieved, but how did they perform? To answer that, here are the Yards Per Play (YPP), Yards Per Play Allowed (YPA) and Net Yards Per Play (Net) numbers for each Pac-12 team. This includes conference play only, with the championship game not included. The teams are sorted by division by Net YPP with conference rank in parentheses.
College football teams play either eight or nine conference games. Consequently, their record in such a small sample may not be indicative of their quality of play. A few fortuitous bounces here or there can be the difference between another ho-hum campaign or a special season. Randomness and other factors outside of our perception play a role in determining the standings. It would be fantastic if college football teams played 100 or even 1000 games. Then we could have a better idea about which teams were really the best. Alas, players would miss too much class time, their bodies would be battered beyond recognition, and I would never leave the couch. As it is, we have to make do with the handful of games teams do play. In those games, we can learn a lot from a team’s YPP. Since 2005, I have collected YPP data for every conference. I use conference games only because teams play such divergent non-conference schedules and the teams within a conference tend to be of similar quality. By running a regression analysis between a team’s Net YPP (the difference between their Yards Per Play and Yards Per Play Allowed) and their conference winning percentage, we can see if Net YPP is a decent predictor of a team’s record. Spoiler alert. It is. For the statistically inclined, the correlation coefficient between a team’s Net YPP in conference play and their conference record is around .66. Since Net YPP is a solid predictor of a team’s conference record, we can use it to identify which teams had a significant disparity between their conference record as predicted by Net YPP and their actual conference record. I used a difference of .200 between predicted and actual winning percentage as the threshold for ‘significant’. Why .200? It is a little arbitrary, but .200 corresponds to a difference of 1.6 games over an eight game conference schedule and 1.8 games over a nine game one. Over or under-performing by more than a game and a half in a small sample seems significant to me. In the 2018 season, which teams in the Pac-12 met this threshold? Here are Pac-12 teams sorted by performance over what would be expected from their Net YPP numbers.
Washington State and Colorado were the only Pac-12 teams that saw their actual record differ significantly from their expected record based on YPP. Washington State exceeded their expected record thanks to a solid record in close games (3-1 in conference play) and the second-best in-conference turnover margin (+5). Meanwhile, Colorado was 1-2 in close conference games and had a -7 turnover margin in conference play. The Buffaloes were particularly bad down the stretch, posting a -12 turnover margin over their final three games. The Buffaloes lost those three games by an average of nearly twenty points, despite a relatively modest per play differential (-.39).

Maybe Pump the Brakes on Washington State
The 2018 season was one of the best in Washington State history. Their eleven wins were the most in school history, their SRS of 12.19 was the eighth best in school history (fifth best since World War II), and their final AP rank of tenth was tied for third. And the Cougars accomplished all this despite dubious preseason expectations. The Cougars were not ranked in the preseason poll and some of the sharpest prognosticators in the college football business (yours truly included) thought they would lose their season opener to Wyoming. A few weeks ago, I offered fans of Auburn, Miami, and Wisconsin hope heading into 2019. Teams that start the season ranked in the top-ten of the AP Poll and wind up unranked tend to bounce back the following season. Now I want to look at the converse (or is it inverse? I never payed close attention in geometry or philosophy). How do teams that start out unranked and finish in the top-ten perform the next season?

From 2005-2017, 27 teams began the year unranked and finished in the top-ten of the final AP Poll. They are listed in the table below along with their regular season record in the year they finished ranked, their regular season record the next season, and the difference in record between the two seasons.
The obvious takeaway from this table is that regression is a cruel mistress. As a general rule, those teams that start out unranked and finish in the top-ten tend to regress the next season. For your convenience, I have summarized the results.
Nearly three quarters of those teams declined the following season, about twenty percent held steady, and less than ten percent improved. Teams were over twice as likely to decline by two games (59%) as they were to stay the same or improve (26%). Cumulatively, the teams saw their regular season record decline by a little more than two games the next season. With this in mind, it might be a good idea to downgrade the Cougars a bit when projecting their 2019 record. But the Cougars were not the only team to finish in the top-ten despite modest preseason expectations.
The way a team finishes the season significantly impacts the way we view their body of work. Florida closed the 2018 season winning four straight, with the last two coming in blowout fashion against Florida State and Michigan. It’s easy to forget that Florida also lost to Kentucky for the first time since the Reagan administration, were not even ranked for good until the first week of October, and lost by three touchdowns at home to Missouri. The Gators recruit significantly better than Washington State, so their program has a sturdier frame, but they also play in the SEC which means they will face a more arduous schedule. I expect to hear and read a lot of Florida darkhorse hype over the summer, but I would be wary of proclamations of their return to glory just yet.

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