College Football Playoffs 2015: Power Ranking Best Defenses in Semifinals

The defensive stars might not be as popular on college campuses as the quarterbacks, but they are the ones who bring home championships.

Well, all football players are popular on college campuses, but they are much more noteworthy while playing as a unit on a successful team.

While all four teams still in contention for a national championship rank in the top 30 in FBS in points allowed per game, there is a big difference between each squad. Some get by with defense while others dominate with it. 

Although success on this side of the ball won't necessarily guarantee a win, here is a breakdown of the top defenses competing in the College Football Playoff.

4. Oregon

The Pac-12 is known for its passing and high-scoring offenses, but that doesn't excuse Oregon's struggles through the air.

Despite keeping teams out of the end zone for the most part, the Ducks still allowed 259.5 passing yards per game this season. That ranks outside of the top 100 in FBS.

To make matters worse, Oregon will have to compete in the Rose Bowl without All-American cornerback Ifo Ekpre-Olomu, who sustained a knee injury in practice. Defensive coordinator Don Pellum discussed impact this injury had on the team, via Andrew Greif of The Oregonian:

"

Anytime someone gets injured it's hard. It's hard. It's like your brother or your sister or your mom or your dad or one of your very close relatives got hurt. It's hard. You've got to deal with that, got to look at it, got to internalize it and then the next day you've got to go out and go fight for him. You've got to put him on your back, you gotta carry him and fight for him. That's what we've got to do, go fight for Ifo and all the guys who got hurt this year.

"

Oregon still has veteran contributors in the secondary like Troy Hill and Erick Dargan, each of whom can step up to replace Ekpre-Olomu. However, taking an elite player off a unit that was already struggling is recipe for disaster.

Compared to the rest of the teams competing in the playoffs, the Ducks are clearly a step behind.

3. Florida State

Phelan M. Ebenhack/Associated Press

Florida State exemplifies the idea of the "bend but don't break" defense. The squad allowed 378.3 yards per game this season and had some bad games on the scoreboard. However, it always seemed to come through when it mattered.

This team forces a lot of turnovers (24 on the season) and steps up when opponents get close to the end zone.

The Seminoles allowed teams into the red zone 48 times but only gave up touchdowns in 25 of those possessions. Adding in 10 field goals, they rank 11th in the nation with scores allowed on just 72.9 percent of red zone appearances.

Most importantly, the squad is simply loaded with talent. Defensive linemen Eddie Goldman and Mario Edwards are certain to be playing on Sundays, and so are cornerbacks P.J. Williams and Ronald Darby. Still, the most impactful player on defense is safety Jalen Ramsey. 

Brendan Sonnone of the Orlando Sentinel discussed the sophomore's role on the team:

Ramsey can line up deep in the secondary or just off the line, racking up interceptions, sacks and everything in between. His play on the team is a major reason the squad is still undefeated, and he will be very important against Oregon.

2. Ohio State

Jay LaPrete/Associated Press

The first thing you notice when you watch Ohio State is the dominant defensive line.

Joey Bosa earned first-team All-American honors after totaling 20 tackles for loss and 13.5 sacks for this defense, but he wasn't alone. Michael Bennett and Adolphus Washington, plus linebacker Darron Lee, help create one of the best pass-rushing teams around.

This pressure toward the quarterback helps the unit rank 15th in the country with just 188.2 passing yards allowed per game. Opposing passers have only managed an efficiency rating of 103.7, which is fifth best in college football.

Alabama offensive coordinator Lane Kiffin is certainly expecting a challenge in the Sugar Bowl:

With impact players at each level like linebacker Joshua Perry and cornerback Doran Grant, this unit can hang with just about any defense in the nation. Of course, containing Alabama's offense will be a challenge on its own.

1. Alabama

There is a reason Alabama ranks among the best in the nation while allowing just 16.6 points per game.

Opponents can't even considering running against this unit. The Crimson Tide are averaging just 88.7 yards allowed per game at 2.81 yards per carry with three total touchdowns on the ground. All of these marks are the best in the nation.

While the program is used to having future NFL stars along the defensive line, staying in there every play to shut down the opposition, this season has been different. Head coach Nick Saban has decided to use more of a rotation, and now the deep roster is wearing down offensive lines.

Ohio State coach Urban Meyer knows this will be a tough task for his players in the next game:

Of course, this squad is not completely unbeatable. Auburn scored 44 points against Alabama in the Iron Bowl behind a great passing day by Nick Marshall. If the Alabama secondary is not prepared, Ohio State can do the same.

However, All-American safety Landon Collins has learned from this experience and should be ready to patrol the defensive going forward. Cornerback Cyrus Jones will also make an impact as the Tide try to ride the elite defense to another national championship.

Unless otherwise noted, all stats courtesy of NCAA.com.

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