Turnover Margin vs. Winning Percentage

It always bugs me when football pundits list turnovers as a "key to the game." Of course it is. They might as well put a spotlight on throwing and catching. While it's obvious that a positive turnover margin will help a team win more games over the course of a season, I thought it would be worth our time to examine just how much it helps.

This chart shows how turnover margin correlates to winning percentage over the past four seasons in college football (2009 - 2012). Each dot represents a team in that four-year period. Per-game turnover margin is on the X-axis and winning percentage is on the Y-axis:

Screenshot240_medium

It's not shocking to see that on average, a higher per-game turnover margin leads to more wins. The relationship is somewhat strong, but obviously there are many other factors that go into winning percentage. The R squared (coefficient of determination) for the trendline shown in the chart is 37%, meaning that turnovers "explain" 37% of the win total data in this model.

The trendline gives us a formula that tells us how many wins a team with a turnover margin of "x" should achieve given the historical data. I adjusted the formula's output from a winning percentage to number of wins in a 12-game schedule:

Turnover Margin Reg. Season Wins
-2.1 1
-1.7 2
-1.3 3
-0.9 4
-0.5 5
-0.1 6
0.3 7
0.7 8
1.1 9
1.5 10
1.9 11
2.3 12

So if your team averages a turnover margin of around +1, you can expect them to win around 8-9 games (all other things equal -- and they never are). I think the best way to look at this is as follows. Let's say your team is talented enough to win around 6 games. For every 0.5 in turnover margin that they are able to achieve, you can expect around 1.25 extra wins.

Given the formula from the chart, we can determine how many games each team should have won in a season based solely on their turnover margin. Going further, we can see which teams over- or under-achieved their projected win total. Let's look at the top/bottom 20 achievers from the 2012 season...

Top 20 Overachievers:

Rk) Team TO Margin Proj. Wins Act. Wins Diff
1) Florida St. -0.43 6.0 12 6.0
2) Texas A&M -0.38 5.7 11 5.3
3) Nebraska -0.86 4.7 10 5.3
4) Ohio St. 0.25 6.8 12 5.2
5) Utah St. -0.08 6.5 11 4.5
6) Oklahoma -0.31 5.9 10 4.1
7) Texas Tech -1.00 4.0 8 4.0
8) Clemson 0.15 7.1 11 3.9
9) Notre Dame 0.62 8.4 12 3.6
10) South Carolina 0.31 7.6 11 3.4
11) Northern Ill. 0.50 8.7 12 3.3
12) Michigan -0.69 4.8 8 3.2
13) Tulsa 0.21 7.9 11 3.1
14) Ball St. -0.23 6.1 9 2.9
15) Stanford 0.64 9.1 12 2.9
16) Alabama 1.00 10.2 13 2.8
17) San Jose St. 0.62 8.4 11 2.6
18) La.-Lafayette -0.08 6.5 9 2.5
19) Georgia 0.79 9.6 12 2.4
20) Vanderbilt 0.00 6.7 9 2.3

Top 20 Underachievers:

Rk) Team TO Margin Proj. Wins Act. Wins Diff
101) Mississippi St. 1.23 10.1 8 -2.1
102) Akron -1.17 3.3 1 -2.3
103) Tulane -0.75 4.3 2 -2.3
104) FIU -0.33 5.4 3 -2.4
104) UTEP -0.33 5.4 3 -2.4
106) North Texas 0.08 6.4 4 -2.4
107) Army -0.67 4.5 2 -2.5
108) SMU 1.08 9.7 7 -2.7
109) Fla. Atlantic -0.17 5.8 3 -2.8
110) Southern Miss. -1.33 2.8 0 -2.8
111) Wake Forest 0.67 7.9 5 -2.9
112) Boston College -0.42 5.1 2 -3.1
112) Eastern Mich. -0.42 5.1 2 -3.1
114) Pittsburgh 0.92 9.3 6 -3.3
115) Kentucky -0.33 5.4 2 -3.4
116) UNLV -0.46 5.5 2 -3.5
117) Wyoming 0.58 7.7 4 -3.7
118) Kansas -0.25 5.6 1 -4.6
119) Iowa 1.00 8.7 4 -4.7
120) New Mexico 0.85 9.0 4 -5.0

So what does it mean if a team wins more games that the turnover margin formula says they should? Good coaching? Talent overcoming adversity? Dumb luck? I think there are so many factors that go into a small sample size college football season that it's difficult to isolate a definitive answer here, but let's take a look at the programs that have overachieved their projected wins in each of the last four seasons:

Overachievers - 4 years in a row: (actual wins - projected wins)

Team 2009 2010 2011 2012 Avg
Nebraska 1.7 3.0 2.5 5.3 3.1
Oklahoma 0.4 1.8 3.7 4.1 2.5
Stanford 1.3 2.5 3.2 2.9 2.5
Alabama 2.8 0.7 3.6 2.8 2.5
Michigan 1.3 2.4 2.8 3.2 2.4
Boise St. 2.3 3.6 3.6 0.1 2.4
South Carolina 1.1 1.8 3.2 3.4 2.4
Oregon 2.9 2.5 2.9 0.9 2.3
Florida 4.3 0.9 2.8 1.1 2.3
Florida St. 0.1 0.9 1.4 6.0 2.1
Nevada 1.9 4.7 0.3 1.1 2.0
Texas 3.9 1.3 1.3 1.2 1.9
USC 2.3 0.4 4.0 0.7 1.9
Cincinnati 3.4 1.0 0.7 1.4 1.6
Oklahoma St. 2.3 1.7 0.9 1.3 1.5
Wisconsin 2.6 1.3 0.4 0.1 1.1
North Carolina 0.9 1.1 0.7 0.3 0.7

That's a pretty solid group of programs. I would argue that it's pretty simple -- good teams have the talent and the coaching to overcome a few turnovers.

Okay...we have to do this now, don't we?

Underachievers - 4 years in a row: (actual wins - projected wins)

Team 2009 2010 2011 2012 Avg
Tennessee -0.4 -1.6 -1.2 -0.1 -0.8
Duke -1.6 -0.9 -1.3 -1.1 -1.2
Minnesota -0.5 -3.6 -1.5 -0.3 -1.5
Kent St. -0.8 -1.2 -3.7 -0.5 -1.5
Colorado -1.9 -1.2 -2.9 -1.2 -1.8
UAB -3.1 -0.9 -2.1 -1.3 -1.9
Rice -2.3 -0.7 -3.9 -0.8 -1.9
Fla. Atlantic -1.4 -0.3 -3.3 -2.8 -2.0
New Mexico St. -1.6 -2.9 -2.1 -1.4 -2.0
Colorado St. -3.2 -1.5 -2.4 -1.1 -2.1
Wyoming -1.4 -2.6 -1.3 -3.7 -2.2
Maryland -2.9 -0.9 -5.0 -0.1 -2.2
Wake Forest -0.4 -3.2 -2.6 -2.9 -2.3
Army -2.3 -3.1 -1.3 -2.5 -2.3
North Texas -1.3 -2.6 -3.1 -2.4 -2.3
Kansas -0.1 -1.5 -3.1 -4.6 -2.3
Washington St. -3.7 -4.0 -1.4 -1.3 -2.6
Akron -2.1 -3.9 -3.3 -2.3 -2.9
UNLV -0.6 -4.5 -4.8 -3.5 -3.3
Memphis -2.3 -2.5 -6.7 -2.0 -3.4
New Mexico -3.9 -2.7 -3.5 -5.0 -3.8

Just in case you're interested in the extremes:

2009-2012

Top 5 highest turnover margins:
+1.69 (2009 Air Force, 8-5)
+1.62 (2012 Oregon, 12-1)
+1.62 (2011 Oklahoma State, 12-1)
+1.54 (2012 Boise State, 11-2)
+1.54 (2009 Rutgers, 9-4)

Top 5 lowest turnover margin:
-2.00 (2009 Miami OH, 1-11)*
-1.58 (2012 Colorado, 1-11)
-1.58 (2012 South Florida, 3-9)
-1.58 (2012 Arkansas, 4-8)
-1.50 (2012 New Mexico State, 1-11)

*This is just insane. -2 per game! This team gained 12 turnovers and lost 36. What a miserable season.

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