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:
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.
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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