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Daniel Wilco | | November 7, 2018

Yes, defense really does win championships in college football, according to the data

Alabama football defense Alabama's defense has been ranked No. 1 in the FBS twice in the past four years. They made the championship game each year, and it's no coincidence.

Defense wins championships. It's a cliche, but, to use another cliche, does it hold any water? Yes, according to the four years-worth of data in the College Football Playoff era. Let’s dig in.

First, how big of a role does defense play in winning in the first place?

To answer that, we looked at the correlation between points allowed and win percentage, to find out how strong a relationship the two statistics have. 

Not surprisingly, points allowed has a strong inverse relationship with win percentage. In other words, the fewer points you allow, the more wins you'll get. Here’s what that looks like in a scatter plot, with each team since 2014 represented by a dot, and teams that made the CFP depicted as red dots:

Defense scatter plot

Click here to view the full chart

There are a few noticeable outliers there. That lone blue dot all the way on the right side of the plot is UCF in 2017. The Knights gave up 25.3 points per game, yet finished undefeated. In the four years of the CFP’s history, 2017 UCF is the only FBS team to go undefeated. They’re also one of just two teams to give up 25 points and win 90 percent of its games. The other is Florida State in 2014, which went 13-1 — allowing 25.6 points per game — and lost in the College Football Playoff semifinal.

Another one that stands out is in the lower left corner of the chart — Boston College in 2015. The Eagles gave up just 15.3 points per game (the 10th fewest PPG of the 514 teams in this time span), but went 3-9 overall, and 0-8 in ACC play.

Alabama is the team of the week

Let’s narrow the focus a bit now. What do these trends look like for College Football Playoff teams? Since the CFP was established in 2014, 16 teams have made the playoff.

The average points allowed for all FBS teams since 2014 is 27.8 per game. The 16 teams that have made the CFP averaged 19 per game, markedly better. The average rank for a CFP defense is 18th.

There are exceptions, of course. In 2017, Oklahoma made the College Football Playoff while allowing 27.1 points per game, ranked 68th in the FBS. Both of those are record highs among the 16 teams. To make up for it, the Sooners scored 45.1 points per game, ranked No. 3 out of 130, but they would give up the most offense all season when they lost to Georgia in the Rose Bowl, 54-48.

Here’s where all 16 teams fall:

Year Team Opp. PPG Defense rank CFP result
2014 Ohio State 22 26 Champion
2014 Alabama 18.4 6 Runner-up
2014 Oregon 23.6 30 Semifinal
2014 Florida State 25.6 49 Semifinal
2015 Alabama 15.1 2 Champion
2015 Oklahoma 22 28 Runner-up
2015 Michigan State 21.7 24 Semifinal
2015 Clemson 21.7 24 Semifinal
2016 Clemson 18 10 Champion
2016 Washington 17.7 8 Runner-up
2016 Alabama 13 1 Semifinal
2016 Ohio State 15.5 3 Semifinal
2017 Georgia 16.4 6 Champion
2017 Alabama 11.9 1 Runner-up
2017 Clemson 13.6 2 Semifinal
2017 Oklahoma 27.1 68 Semifinal

You’ll notice that the No. 1 defense in the country made the CFP in only two years: Alabama in 2016, and Alabama in 2017.

In 2014, Ole Miss finished with the top defensive unit, allowing just 16 points per game.
Another interesting fact from that, the top defense in the country has allowed fewer points each year, from 16 per game in 2014, to 11.9 in 2017. 

And once the Playoff is set, defense still pays off. Three of the four CFP champions ranked in the Top 10 in the nation in points allowed, with Ohio State in 2014 as the lone exception. The Buckeyes’ opponents averaged 22 points per game that season, ranked 26th in the FBS. But they also scored 44.8 points per game — the fifth-most in the country.

So what does this mean for this year?

RELATED: College Football Playoff rankings: Notre Dame takes LSU’s spot, Michigan jumps to No. 4

The top four teams in the College Football Playoff Ranking on Nov. 6 all sat within the top 20 defenses through nine games:

CFP rank (Nov. 6) Team PPG Rank
1 Alabama 14.1 7
2 Clemson 13.3 4
3 Notre Dame 19.3 19
4 Michigan 13.6 5
5 Georgia 16.4 10
6 Oklahoma 27.9 73
7 LSU 16.7 11
8 Washington State 23.8 45
9 West Virginia 22.3 35
10 Ohio State 23.8 45
11 Kentucky 15.3 8
12 UCF 20.9 24
13 Syracuse 28.1 76
14 North Carolina State 25.5 59
15 Florida 21.1 26
16 Mississippi State 12.3 2
17 Boston College 24.1 47
18 Michigan State 19.0 16
19 Texas 26.8 66
20 Penn State 24.4 49
21 Iowa 18.6 14
22 Iowa State 21.3 27
23 Fresno State 12.3 2
24 Auburn 17.3 13
25 Washington 16.0 9

Georgia, currently ranked No. 5 in the CFP poll is at No. 10 in the country, with just 16.4 points allowed per game. But Oklahoma, at No. 6, is tied for 73rd in the nation in defense, allowing 27.9 points per game. If the Sooners did make the Playoff with those numbers, they’d both be records.

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