USF's new Defensive Coordinator Tom Allen came from Ole Miss, where he was the Linebackers Coach and Special Teams Coordinator. The Rebels' 4-2-5 scheme was the best regular season defense in the country last year, and carried the team to a #3 ranking for a few weeks. Then they lost a few games and finally got blown out 42-3 by TCU in the Peach Bowl. Coincidentally, the Horned Frogs also do the 4-2-5.
The increased use of the 4-2-5 has grown out of the need to match up against spread offenses, and it is philosophically similar to the spread. Traditional offenses and defenses tend to come down to size and strength. The team with the bigger and stronger players has always been more likely to win. A spread offense uses speed and misdirection to even the playing field against defenders that may be bigger and stronger than their offensive counterparts. A few good skill players, like a running quarterback and an agile Z receiver, can tear up a traditional 4-3-4 defense no matter how big and strong the linemen and linebackers are. The 4-2-5 has a similar underlying point of view. Skill players are essential and they do not need to be big, they just need to be fast and in the right position.
USF's linemen and linebackers are well-suited for the 4-2-5. Defensive tackles Derrick Calloway and Deadrin Senat, along with end Eric Lee, will have the same job they have always had. Senat is the nose tackle, and at 300 pounds he should get double-teamed on every play like Todd Chandler did last year. The other defensive end, former linebacker Josh Black, will play the "bull" position, from which he will sometimes cover the running back instead of rushing the quarterback.
Auggie Sanchez is the strong side linebacker. He will read the offensive backfield, cover against the run, and cover tight ends in a small zone. Nigel Harris will play the weak side "stinger" position, where he will be responsible for covering running backs and quarterbacks who may end up with the ball. The stinger will be relatively free to go where he wants and disrupt the play. This is a perfect job for Nigel Harris, who forced six fumbles last year.
The front six will naturally be trying to tackle anyone with the ball, but as long as they don't let rushers get through the middle, they will be doing their jobs. A jet sweep or bubble screen is not their responsibility. As soon as the linebackers and linemen see a run developing, they need to push the play horizontally so that the safeties have time to come up and make tackles near the sidelines. You know those plays where even a great running back can't find a gap up the middle so he moves laterally and tries to turn the corner just as a swarm of defensive backs arrives? That's what Tom Allen wants to see.
The safeties (Nate Godwin and Tajee Fullwood) are basically doing an old-fashioned cover 2 scheme, where they play the deep zones and everyone else is on man-to-man. The husky (Jamie Byrd) covers the slot receiver or H-back, who often tries to find the seam between the safeties. So the husky frequently ends up in the middle of the field covering the soft spot. This is more or less a cover 2 robber, where the Husky is the nickel back.
Johnny Ward and Lamar Robbins are the cornerbacks, and they both have enough real game experience to deserve some confidence. They need to be really good this year, because they will cover the X and Z receivers, who are the #1 receivers on their respective sides. The corners play the #1's man-to-man unless they run a curl or flat route. In this case, the corner usually switches responsibilities with the nearest safety, who would be covering the #2 receiver (either the Y tight end or slot man). The idea here is that the safety can come over in front of the #1 receiver and break up or intercept the pass easier than the cornerback can, who would now be upfield from where the pass may be caught. If the pass is caught, the cornerback is still in position to make a tackle. It will appear to the quarterback that his #1 has evaded the cornerback and he may be tempted to throw in that direction before he realizes that the safety is actually covering the #1.
Defensive backs swapping responsibilities like this is based on techniques like banjo and robber, so it doesn't look radically different from what has been done before. But it does confuse quarterbacks because it is sort of a mix of zone and man coverage. In fact, one of the main advantages of this defense is that it's difficult for the opposing team to read. The field is split in half for the defense, with a corner, safety and husky on the strong side and a corner and safety on the weak side. One side of the defense might do the banjo thing while the other side just does man coverage. One side might be doing a read technique while the other side does a robber technique. When executed correctly, all of this provokes uncertainty in quarterbacks and receivers.
Of course blitzing is an important part of this defense. The most basic blitz involves sending in both linebackers, in which case all of the DBs will play man-to-man on their receivers. Switching to man coverage all over also makes the scheme harder to read for the opposing team. The husky will blitz a lot too, and give his coverage responsibility to the strong safety.
The main weakness of the 4-2-5 is runs up the gut. Without a third linebacker, there can be a crack in the middle of this defense for a good power team. This is a problem for all teams that do a 4-2-5, and often they will throw in another linebacker and basically do a 4-3-4 if they are playing a power run squad. The Bulls' third linebacker will probably be Tashon Whitehurst, when needed.
The main defensive problem that USF will face in 2015 is simple mistakes. The defense is new and there is bound to be confusion. The corners and safeties need to communicate with each other; if they don't they will give up big plays. The linebackers need to keep an eagle eye on the ball or else they will neither be covering the pass nor getting to the rusher. Expect to see some of that as the season begins. What should be evident is the defense's improvement as the season goes on. The system will become second nature as the players gain real experience with it, and they should be giving up fewer and fewer yards each game.