First Half Point Differential Part I: An Introduction

The primary reason I started this blog nearly fifteen years ago was to make predictions. In that decade and a half, I have made a lot of them. Some good, and some not so good. In my never ending quest to make better predictions, I try to think of stats that can identify teams poised for positive and negative regression. My offseason posts on Yards per Play (YPP) and the Adjusted Pythagorean Record (APR) are two that I am quite proud of. I don't want to spoil the rest of the post, but I think I have found another: first half point differential.

So what is first half point differential (1HPD)? Unlike advanced stats, it is easy to define and calculate. It is simply the scoring margin (positive or negative) in the first half of a game. In the 2019 College Football National Championship Game, LSU led Clemson 28-17 at the half. The 1HPD for LSU was +11 and -11 for Clemson. Simple stuff. With more than ample time on my hands, I calculated the 1HPD for all FBS teams in conference play back to the first season of the College Football Playoff (2014). That is six seasons worth of data. What did that data show? I thought you would never ask.

For starters, 1HPD in conference play is positively correlated to a team's conference record. In fact, with an R squared value of .72, the correlation is stronger than YPP in conference play (which surprised me). So if 1HPD has a strong correlation with conference success, what happened to those teams that saw their expected record based on 1HPD differ significantly from their actual record? Wow, its like your reading my mind.

For YPP, I consider a difference of .200 between actual and expected record significant, so I used the same logic here. Between 2014 and 2018 101 FBS teams saw their actual record differ significantly from their expected record. 52 teams under-performed relative to their expected record and 49 exceeded their expected record. Those teams that under-performed tended to see their conference record improve the next season.

The average team improved by 1.41 wins in conference play and nearly 70% of the teams improved by at least one win.

On the other hand, the teams that exceeded their expected record more often than not declined the following season.

The average team won about 1.80 fewer games the next season and more than three quarters of the teams declined by at least one win.

It certainly appears 1HPD is a solid way to identify teams that might regress or rebound the next season. Intrepid readers might recall the title of this post and wonder what comes next. Well, next Thursday, I'll give you a rundown of the 1HPD for Group of 5 teams from 2019 and try to identify some teams to watch assuming we have a season in 2020. In two weeks, we'll look at the Power 5 and then in three weeks we'll see if 1HPD can be used to handicap conference title games and the College Football Playoff. Stay tuned!

2019 Adjusted Pythagorean Record: Sun Belt

Last week we looked at how Sun Belt teams fared in terms of yards per play. This week, we turn our attention to how the season played out in terms of the Adjusted Pythagorean Record, or APR. For an in-depth look at APR, click here. If you didn’t feel like clicking, here is the Reader’s Digest version. APR looks at how well a team scores and prevents touchdowns. Non-offensive touchdowns, field goals, extra points, and safeties are excluded. The ratio of offensive touchdowns to touchdowns allowed is converted into a winning percentage. Pretty simple actually.

Once again, here are the 2019 Sun Belt standings.

And here are the APR standings with conference rank in offensive touchdowns, touchdowns allowed, and APR in parentheses. This includes conference games only with the championship game excluded.

Finally, Sun Belt teams are sorted by the difference between their actual number of wins and their expected number of wins according to APR.

I use a game and a half as an arbitrary threshold to determine if a team significantly over or underperformed relative to their APR. By that standard, Arkansas State significantly exceeded their APR. The Red Wolves finished 4-1 in close conference games, meaning eighty percent of their league wins came by a touchdown or less. South Alabama significantly undershot their expected record based on APR. They also underperformed relative to their expected record based on YPP and we went over some reasons for that last week.

Paul Petrino: The Sun Belt Savant
Even hardcore college football fans may have a hard time recalling Paul Petrino. They are probably intimately familiar with his brother, but like Bill Dooley, Paul is often overshadowed by his sibling. This is doubly true now that Idaho has dropped down to the FCS level. Despite the fact that Idaho no longer plays in the FBS, I like to highlight forgotten or overlooked greatness on this blog, and Paul Petrino's Against the Spread (ATS) record in the Sun Belt is one for the ages.

Before we dive into Petrino's ATS mark as head coach of the Vandals, here is a quick history of Idaho's nomadic existence since they returned to FBS in 1996. The Vandals played in the Big West for five seasons (1996-2000) before becoming a charter member of the Sun Belt in 2001. They only lasted four seasons in the fledgling conference before joining the WAC in 2005. The Vandals stayed in the WAC until the conference dissolved following the 2012 season. They played as an independent for one season before rejoining the Sun Belt in 2014. After four seasons, they dropped down to the FCS level where they currently reside in the Big Sky Conference. Petrino coached the team for the entirety of their second run in the Sun Belt (and their one season as an independent). During those four seasons, the Vandals did not post a great Sun Belt record, finishing 13-19 in league play. They did win six games league games in 2016, but in the other three seasons, their conference record was 7-17. However, even though they weren't winning games on the field, they were cleaning up for those brave enough to bet on them in Sun Belt games.

From 2014-2017, Idaho posted a phenomenal ATS record of 24-8 in conference play. That was by far the best of any Sun Belt team in that span.

The Vandals were especially good on the road, failing to cover just once in an away conference game over those four seasons.

This amazing ATS run is likely just a lot of noise and randomness. Idaho was just 5-7 ATS in non-conference games over the same time period. I doubt Petrino had a horseshoe or other lucky trinket he deployed specifically for conference games. Still, this is further proof that amazing things happen all the time in college football if you know where to look. A coach with a receding hairline, a much famous older brother, and a career record of 28-55 was a veritable ATM for degenerates a few seasons ago.

That concludes our YPP and APR rundowns of the 2019 season. I hope we get to do this for 2020, but I have my doubts. As a resident of South Carolina, it pains me to say I have probably seen more folks with Confederate memorabilia than masks on my trips to the grocery and drug stores. Another spike in infections could certainly jeopardize the 2020 season, not to mention the health of many people in this nation. If we don't get a 2020 season, I think I will do weekly YPP and APR lookbacks at other seasons. I have only been doing them since 2015, so we missed out on a lot. Want to know how YPP saw the SEC in 2005 or how APR saw the Big East in 2007? If the 2020 season is canceled, that will be your consolation. In the meantime, content will be sporadic on the blog over the summer. I'm working on a few projects, so there will be posts, just not weekly. Check back every now and then, and as always, thanks for reading.