The Horned Frog defense is first in the nation in scoring defense, allowing 9.3 points per game, and second in total defense, giving up just 218.3 yards per game. But the numbers that make Gary Patterson’s defense unique are four, two and five.

The 4-2-5 defense is a rarity in football because it deploys five defensive backs, whereas more common base defenses like a 3-4 or 4-3 use only four. John Denton, radio analyst for the TCU/ISP Sports Network, said the 4-2-5 allows the Frogs to keep pace with opposing offenses.

“It does put a lot of speed on the field,” he said. “It gives you a lot of variability and it also gives you the ability to adjust on the fly if you see different formations.”

Last second adjustments are something that an offense usually uses to gain an advantage on the defense, Denton said. That is not the case with Patterson’s scheme.

“A lot of what’s fun to watch about the 4-2-5 is that it’s as much like an offense as it is a defense because you see Gary and the staff, they wait to see the personnel set that the opponent is going to give them,” Denton said.

Some of the rotating personnel has been a result of injuries. Weak safety Alex Ibiloye and strong safety Tyler Luttrell have missed time because of injuries, but Tekerrein Cuba and Colin Jones have filled in for them so well that it has not made a difference, free safety Tejay Johnson said.

“Our whole deal is prepare as if you are going to be a starter,” Johnson said. “So we don’t expect any let down when we rotate people in to play. We expect you to play just as well as the person you’re rotating in for.”

The 4-2-5 relies on cornerbacks playing man-to-man coverage on wide receivers. Greg McCoy and Jason Teague, who has allowed only one catch this season, replaced four year starters Rafael Priest and Nick Sanders at the two cornerback positions this season. Both have played well, Patterson said.

“When you have a guy at the boundary that has only allowed one catch and that’s where you play a lot of your one-on-one coverage, which everybody in our conference knows that and you have a player that can play like that it makes a big difference,” Patterson said.

If it is solid, the man-to-man coverage allows the coaches to send an extra rusher at the quarterback. The defense has sacked the opposing quarterback 19 times this season, led by senior defensive end Wayne Daniels with 5.5 sacks.

“The one thing that the defense has been able to do is pressure the passer, which was a concern because Jerry Hughes and Daryl Washington were going away,” Denton said.

After allowing its first points in three weeks, in a 31-3 win over BYU, the defense will try to stop an Air Force rushing attack Saturday that leads the nation in rushing, at 346.9 yards per game.