Using Point Differential in the NFL

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On last week’s podcast, I mentioned that I had a system that faded lucky teams.  Luck comes in many different forms in the NFL.  There is luck in recovering fumbles, luck in who falls to you in the draft, and luck in a big penalty going your way.  In this instance, I’m actually looking at lucky teams in terms of point differential.  Teams that are barely outscoring their opponent and winning are unlikely to continue to have those games go their way.

The system that I mentioned uses two filters that together can tell a better story about the team’s true talent.  The system uses the team’s actual winning percentage, as well as the team’s pythagorean winning percentage, which is based off of point differential.  Current Bet Labs members can see the full system details in the Think Tank now.

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There is another filter within Bet Labs that combines these two win percentages into a differential called “Pythagorean +/-“.  Using this filter, we can quickly determine which teams are playing better than their expected win percentage based on point differential and vice versa.  A positive number indicates a team’s actual record is worse than their expected record given their point differential.  These teams may be undervalued by bettors and the market and could be in line for some positive regression.

By looking at current game matches, we can easily see every teams’ Pythagorean differential:

pythag-cgm
Using that filter, I can sort to find which teams are overrated and which teams may be underrated.  Let’s look at some teams who apply.

Overrated

Houston Texans  Win %: 62.5  Pythag %: 39.0

The Texans are currently 5-3 and lead the AFC South, but they currently have a point differential of -30 through eight games.  They have yet to win a road game and their home wins only feature one impressive team in Kansas City.  All of that being said, nobody else in the AFC South is really all that good either.  In fact, no team in the AFC South has a positive point differential this season.  Houston isn’t really a 10-win team, but they are still good enough to win a really bad division.

Oakland Raiders  Win %: 75.0  Pythag %: 53.4

Jack Del Rio has gotten some much deserved props for being aggressive in trying to win games and it has helped get the Raiders to a 6-2 record.  While I agree with those coaching decisions, eventually they might not work out every time and some of those close Raiders wins will turn into close Raiders losses.  Oakland has also benefited from an easy schedule as none of their six wins have come against a winning team.  Derek Carr has made the Raiders relevant but it may be time to temper expectations in the Black Hole.

Underrated

Arizona Cardinals  Win %: 42.0  Pythag %: 64.2

Arizona’s playoff chances may be dwindling but they are still expected to be a winning team the rest of the way.  When you look at the Cardinals’ roster, you wonder how they don’t have a better record.  While a lot of their point differential is helped by a blowout against Tampa Bay, it’s still strange to see that Arizona has a better point differential than the Atlanta Falcons.  This team isn’t as bad as their current record indicates but they are running out of time to prove it.

Carolina Panthers  Win %: 28.0  Pythag %: 48.0

Carolina was due for some regression after outperforming all of the peripherals last season, but they have regressed more than anyone expected.  They should be around a .500 team based on point differential but currently sit at 2-5 and dead last in the NFC South.

San Diego Chargers  Win %: 37  Pythag %: 53.5

San Diego has famously lost a bunch of games this season that they had no business losing.  Unfortunately for them, they don’t get a do-over and have three teams ahead of them in the toughest division in football.

Pythagorean records are just another thing I like to analyze when looking at NFL systems in Bet Labs.  You can use these and 200 other filters with a free account at Bet Labs Sports.

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