It seems as if each progressive year is college football's highest-scoring to date. Tempo, yards, and points creep upward, and it becomes more difficult to judge defenses.

In the 1950s, for instance, a top-20 defense might expect to allow 10 points per game. In 2015, that number was closer to 20. At one point, allowing five yards per play was considered a sign of weakness; now, that average would rank in the top 30.

Here is, of course, another area where stats can come in handy. Stats cannot provide end-all, be-all answers, but they can define a baseline for us, and they can add proper context to a team's accomplishments.

This week, I've been using my estimated S&P+ ratings for previous seasons to celebrate some of college football's best-ever programs, offenses, and matchups.

Now let's see what these numbers can tell us about great defense. Which defenses were not only good, but excellent enough to stretch to the far end of the bell curve?

Below, we're going to look at 25 of the best defenses in college football history. But we're going to break them into two groups: the 10 best since 2005 and the 15 best from before 2005.

Why the 2005 divider? Teams that played since 2005 are graded using the normal S&P+ formulas. Before 2004, all I have are points scored and points allowed. For these 2005-to-present teams, there is a normal, bell-shaped distribution, meaning most teams rank toward the middle. But for 2004 and before, it's not quite bell-shaped because, well, everybody starts with zero points. The maximum for an offense is limitless, but the minimum is zero no matter what. That means there are more offenses in the 99th percentile or higher than there are defenses.

This suggests an imperfect distribution. And with the normal distribution of the 2005-15 set, if I were to use these percentile grades, it would suggest that four of the top five defenses of all-time have played since 2011. While there have been some incredible recent defenses, I'm guessing that's not actually the case.

So we'll separate them into two piles: 10 defenses you probably remember well and 15 you might not. This list is an attempt to celebrate greatness, and celebrate we will, perfect curve or imperfect curve.

The Top 15 defenses from 1890 to 2004

15. 1959 LSU

When Ole Miss and LSU faced off in their classic Halloween 1959 battle (and again in that season's Sugar Bowl), it was a matchup of two of the best defenses ever. In two games, LSU allowed 24 points to the Rebels; in the other nine games, the Tigers allowed 26 points.

Ole Miss just missed this list because of schedule strength, but the Rebels' numbers were even more impressive: 11 games, 21 points allowed ... seven via Billy Cannon's famous return of a punt that was supposed to bounce out of bounds and 14 via drives that started inside the Ole Miss 10.

14. 1985 Michigan

The 1985 title was decided when No. 2 Miami lost to Tennessee and No. 3 Oklahoma whipped No. 1 Penn State. But the best team of the season might have played earlier on New Year's Day, when Michigan took down Nebraska in the Fiesta Bowl.

Jim Harbaugh captained the offense to 28.5 points per game, but the defense, led by All-Americans Mike Hammerstein and Brad Cochran, allowed just 8.2. They held five opponents to three or fewer points and allowed more than 17 just once (to Nebraska). A 12-10 loss to Iowa and a 3-3 tie against Illinois kept the Wolverines out of title contention, but that wasn't the defense's fault.

13. 1997 Michigan

This defense was so good, it won the Heisman. Corner Charles Woodson was the biggest name, but this unit was loaded, with All-Americans Rob Renes and Glen Steele up front, Sam Sword and Dhani Jones at linebacker, and Andre Weathers, Tommy Hendricks, and Marcus Ray joining Woodson in the back. Michigan allowed just 26 points in its first five games and held Ryan Leaf's Washington State to 16 points in the Rose Bowl.

12. 1992 Arizona

(Eugene Garcia-Getty Images)

Dick Tomey's Desert Swarm was simply untouchable in 1992. The Wildcats allowed a paltry 9.8 points per game despite a pretty tough schedule; against five ranked teams, they allowed a combined 34 points. They gave up just eight points in a one-point loss to No. 1 Miami in September, then just three in a win over No. 1 Washington in November. Only Washington State (23) was able to top 17 points against Brandon Saunders, Tedy Bruschi, Keshon Johnson, and the Wildcats.

11. 1907 Michigan

Fielding Yost's Wolverines began by throttling Case, Michigan State, Wabash, and Ohio State by a combined 99-0, but their biggest statement came on Nov. 2 against Vanderbilt. The Commodores were an offensive machine; they had already put up 40 points on Kentucky and would finish by outscoring Ole Miss, Georgia Tech and Sewanee by a combined 131-12. But against the visiting Wolverines, they couldn't do a damn thing -- Michigan won 8-0.

The scoreless streak ended in the finale. A powerhouse Penn came to Ann Arbor averaging 24 points per game and squeezed out a 6-0 win.

10. 1980 Florida State

(Allen Steele-Getty Images)

Bobby Bowden's awesome Seminoles won two of college football's greatest matchups in 1980 and made their first serious national title threat because of a dominant D. Despite a brutal schedule that featured three top-five opponents and nine teams that won at least seven games, the Seminoles gave up just 8.6 points per game -- 18 per game against three elite teams and 5.4 against everybody else. Defensive coordinator Jack Stanton's Noles recorded 38 sacks, 18 interceptions, and 22 fumble recoveries and held opponents to an anemic 2.4 yards per carry.

Nebraska averaged nearly 40 points per game but eked out just 14 in one of Bowden's first statement wins, an 18-14 victory in Lincoln.

9. 1919 Washington & Jefferson

How does Washington & Jefferson -- a small, private liberal arts college outside of Pittsburgh that dropped from the Division I ranks in 1934 -- make this list? By taking on three strong teams -- Syracuse (11.2 points per game), Pitt (13.2), and WVU (32.6) -- and outscoring them, 19-14. (They also outscored Carnegie Tech and four other non-DI teams, 106-0.) A statistical technicality? Probably.

But the Presidents were in the middle of a hell of a run. They went 75-17-5 from 1912-21 and finished that string by going 10-0-1 and tying mighty California in the Rose Bowl. John Heisman coached there in 1923, as well. Now they're one of the stronger programs in the Division III Presidents' Athletic Conference.

8. 1971 Alabama

Alabama had averaged just seven wins a year from 1967-70, and after finishing in the AP top 10 for nine straight years, they finished unranked in 1969 and 1970. But in 1971, the Tide turned, if you will. (Sorry.)

Not only did the offense erupt as it mastered the wishbone, the defense was suddenly a Bear Bryant defense again. Alabama played four ranked teams in the regular season and allowed 39 points against them; lesser opponents fared even worse, scoring a combined 45 in seven. The season ended with a dud -- a 38-6 shellacking at the hands of undefeated Nebraska in the Orange Bowl -- but this D was as stingy as any Bryant had.

7. 1965 Michigan State

In 1964, Michigan State stumbled to 4-5, allowing nearly 16 points per game, a dreadful average by head coach Duffy Daugherty's standards.

But then Bubba Smith became Bubba Smith. The junior end was maybe the best defensive player in the country, and along with linebacker George Webster and a devastating secondary, Sparty dominated. State didn't allow more than 14 points all year and more than seven only four times. They put themselves on the doorstep of a national title with a 12-3 destruction of Notre Dame before falling to two-touchdown underdog UCLA in a classic Rose Bowl.

6. 1962 LSU

SEC offenses began to improve in the early-1960s, but LSU was as stingy as ever in Charles McClendon's first year. Led by All-American defensive tackle Fred Miller and halfback/defensive back Jerry Stovall, the Tigers lost only to No. 6 Ole Miss by a 15-7 margin. It was the only time all season that they would allow more than seven points. No. 5 Georgia Tech managed seven, and in the Cotton Bowl, No. 4 Texas claimed the same fate as five other 1962 opponents: a shutout loss.

5. 1977 Tennessee State

It is a tantalizing question: How would the great HBCU teams of the 1950s, 1960s, and 1970s have fared against Division I competition? With so much of the South failing to integrate until deep into the '60s, teams in the SWAC and MEAC stockpiled talent but mostly played amongst themselves.

There was a glitch in 1977, however. HBCUs were for a single season denoted as Division I before Division I split into I-A and I-AA. These schools still didn't really play integrated schedules, but they're at least included in the official Division 1 records.

The 1977 Tennessee State team was fantastic. The Tigers went 8-1-1 with shutdown wins over 8-3 Jackson State (17-7) and 10-1 Grambling State (26-8), among others. Only one opponent (Florida A&M) managed more than 14 points.

Another statistical technicality? Almost certainly. But this team featured future second-round draft picks on the defensive line (end Sylvester Hicks, tackle Stan Johnson) and a fourth-round linebacker in Danny Johnson. Whether it was one of the best-ever defenses or not, I guarantee it was one of the best of 1977.

4. 1994 Washington State

(Otto Greule Jr.-Getty Images)

Arizona may have had the cool nickname of Desert Swarm, but Mike Price's 1994 defense was one of the stingiest in Pac-10 history. The Cougars couldn't score to save their lives -- they averaged just 16 points -- but Ron Childs headed up a devastating D that allowed 9.6 points per game against five ranked teams and completely shut down a Baylor team that came into the 1994 Alamo Bowl averaging more than 30 points per game.

3. 1979 Texas

In 1977, Texas was in position to win the national title before falling to Joe Montana and Notre Dame. Two years later, the Longhorns were again stacked, at least on one side. Texas averaged 18.4 points per game (80th in Division I-A) and lost three games as a result.

But the defense was destructive. The 'Horns took on four top-10 opponents and shut all of them down. No. 5 Missouri was shut out, No. 3 Oklahoma managed seven points, No. 10 Arkansas erupted for 17, and prolific No. 5 Houston managed 13.

Riding the bench for that 1977 defense, by the way? Current Texas defensive coordinator Vance Bedford, who would go on to become a two-time all-conference cornerback.

2. 1966 Ole Miss

From the standpoint of pure points allowed, it's hard to top the 1959 Ole Miss team that gave up just 21. But in 1966, as college football offenses were continuing to open up, Ole Miss took on a massive schedule of offenses and still allowed only 65 points.

Alabama scored 17 points on the Rebels in Week 3, and Texas put up 19 in the Bluebonnet Bowl. But in the other nine games, John Vaught's team allowed 29 points. Houston averaged 34 but managed just six. Georgia: 23 per game against everybody else, three against Ole Miss.

The Rebs pitched five shutouts, but like 1979 Texas, the defense's stature wasn't enough to overcome faulty offense. In three losses, the Rebels scored a combined 10 points.

1. 1978 USC

USC has been known for offense, but in 1978, John Robinson fielded one of the best defenses in the sport's history. Scoring averages were rising quickly, but despite a loaded slate of five ranked teams and nine opponents that finished with at least seven wins, a USC D powered by one of the sport's best safety combinations (Dennis Smith, Ronnie Lott) allowed more than 20 points just once.

Eventual national co-champion Alabama averaged more than 30 points against everybody else but managed just 14. Michigan State averaged more than 40 against everybody else but scored nine. Stanford ... Notre Dame ... Michigan ... all had offense-friendly reputations, and none met their averages.

The USC offense wasn't quite as explosive as normal, and it didn't matter. USC went 12-1 because of this dominant unit.

The top 10 defenses from 2005 to 2015

I bet you'll never guess which school is all over the more recent list.

10. 2009 Alabama

(Jeff Gross-Getty Images)

In Nick Saban's first Tuscaloosa season, 2007, Alabama allowed 286 points, a decent 22 per game. In 2008, the Tide allowed 14.3. In 2009, 11.7. It took him a couple of recruiting classes to get all the pieces, but when he did, the titles followed.

The 2009 D featured Rolando McClain, Mark Barron, Javier Arenas, Marcell Dareus, Terrence Cody, etc., and was probably the fourth-best Alabama defense of the last seven years. Ridiculous.

9. 2012 Alabama

In our heads, Texas A&M and Johnny Manziel torched Alabama's defense. But while the Aggies averaged 7.1 yards per play and 44.5 points per game in 2012, they managed only 5.4 and 29 against the ridiculous Bama D. Only by Alabama's standards is that a torching.

In a year of escalating point totals, Alabama allowed more than 14 points in a game three times in 14 tries and allowed more than 300 yards in a game just twice.

That this was the third-best defense of the Saban era is astounding.

8. 2006 Virginia Tech

Frank Beamer and defensive coordinator Bud Foster led defenses that adapted and continued to thrive. But their 2006 unit was particularly ridiculous. The Hokies allowed 11 points per game and held opponents to a paltry 2.8 yards per carry on the ground.

Actually, just pick a random stat. They were all absurd. A 52 percent completion rate (with six touchdown passes to 17 interceptions)? A 27 percent third-down conversion rate? Eight players with at least 6.5 tackles for loss? Brandon Flowers' 21 passes defensed? Tech allowed 69 points against Georgia and Georgia Tech ... and 74 against everybody else on the schedule.

7. 2014 Ole Miss

We know the story. Dominant through the first two months of the season, they suffered a couple of gut-wrenching losses and a season-turning injury to star receiver Laquon Treadwell and limped to a 9-4 finish.

Blame the offense for most of that. The Rebels scored seven or fewer points in three of their four losses. The defense was one of the most successfully aggressive of all time. They picked off 22 passes, recorded 99 tackles for loss, and featured star power at every level, from all-world tackle Robert Nkemdiche to linebacker Serderius Bryant to corner Senquez Golson to safeties Mike Hilton, Cody Prewitt, and Tony Conner.

6. 2009 Nebraska

(Jamie Squire-Getty Images)

I have nothing against Mark Ingram. He was a good running back on an excellent Alabama squad, and by 2009, Alabama probably deserved to have its first Heisman. And I know defensive players don't win the Heisman. I do. Even Charles Woodson had to line up as a receiver a few times to win it.

But the fact that Ndamukong Suh didn't win is one of the biggest travesties in college football awards history.

Suh recorded 24 tackles for loss, 12 sacks, 26 quarterback hurries, 10 pass breakups, one pick, and three blocked kicks in 2009. He was so dominant that NU head coach Bo Pelini was almost able to play a permanent dime formation; Suh was a one-man offensive line destroyer, and Pelini almost never had to blitz. Just drop about seven guys into coverage, then pounce on wayward passes when the quarterback still gets hit in about 1.5 seconds.

Nebrsaka allowed 10.4 points per game and four yards per play. This was a wrecking machine, and it all revolved around a single player.

5. 2012 Michigan State

Michigan State has gone 36-5 since the start of 2013; the defense has carried the water, but the offense was the reason for the breakthrough. You see, the defense was even great during the Spartans' 7-6 2012. The offense was just "Le'Veon Bell left" and "Le'Veon Bell right," and the Spartans averaged 20 points per game.

But the defense kept games close regardless. Linebackers Max Bullough and Denicos Allen combined for 22.5 tackles for loss, end William Gholston chipped in with 13 more, and a secondary led by Johnny Adams and Darqueze Dennard allowed a passer rating of just 98.8.

4. 2011 LSU

Tyrann Mathieu. Morris Claiborne. Eric Reid. Tharold Simon. Ron Brooks. Brandon Taylor. If Nebraska's 2009 defense was built around a dominant lineman, LSU's even more dominant unit was built around one of the best secondaries of modern times.

At 5'9, 175, Mathieu would have been small for a safety in the 1950s, but football has rarely seen a playmaker like him. He recorded 7.5 tackles for loss, six forced fumbles, four fumble recoveries, two interceptions, and nine pass breakups, and he returned two punts for touchdowns. Without a single rushing or receiving yard, he scored 24 points. Opponents scored 24 points on LSU in a game just once.

3. 2012 Florida

Florida scored just 20 points against Manziel's Texas A&M and won. The Gators scored 14 on LSU and won. They scored 14 on Missouri and won. They averaged a decent-at-best 5.3 yards per play with a freshman quarterback and went 11-2 all the same.

Nobody could move the ball on a defense that featured Dominique Easley, Dante Fowler Jr. and Sharrif Floyd up front, Jon Bostic and Jelani Jenkins at linebacker, and Matt Elam and Jaylen Watkins in the secondary. This was Will Muschamp's beautiful, ugly dream of a team. But it could only last one season before the ugly overpowered the defensive dominance.

2. 2015 Alabama

(Jerome Miron-USA TODAY Sports)

It's a shame Alabama's dynasty is dead.

1. 2011 Alabama

(Ronald Martinez-Getty Images))

Here's how good the 2011 defense was.

Against teams not named Alabama, LSU averaged 40.9 points, produced a passer rating of 156.5, and featured four running backs who combined for 184 rushing yards per game and 5.5 yards per carry. Yes, the defense set the offense up for success, but this was a sound offense that ranked 13th in Off. S&P+.

Now think about your own perception of that LSU offense. Because of what Alabama did, first in a 9-6 loss in Tuscaloosa, then in 21-0 destruction in the BCS title game, the Tiger O has been forever labeled as a unit that was mediocre at best, one that drastically held back a good defense. In two full games (and an overtime!) against Alabama, this strong offense scored nine points and gained 321 yards. In 2011, Alabama allowed more than 251 yards, 4.4 yards per play, or 14 points just one time, and that was against Georgia Southern.

That's how good the 2011 Alabama defense was.