If you ask most defensive coordinators what type of offense they like to face the least, you'll get one of two answers, either the Airraid of Mike Leach, or a triple option (veer) team. Lets be clear, the option is as old as football and will always be here. Florida's whole offense is essentially option, but based in shotgun and spread formations. RichRod's offense was a spread option and we know how well that worked for us with Woody Dantzler, so anyone who will tell you the option is dead or outdated is really an idiot who doesnt pay attention to football.
The Flexbone is derived from Fisher DeBerry's comment, "We need to become more flexible in the Bone..." DeBerry was talking about adding passing concepts to his normal Wishbone offense, and the flex is essentially the first true "spread option." The whole purpose of flexing the TE out was to create a horizontal stretch to the defense (Flexing essentially means the TE is lined up offset within 2 yards of the OT, and standing him up). Clemson puts WRs and TEs in flex positions frequently, yet we never really throw to the TE (the tragedy of Ben Hall).
In GT's Flex, those flexed TEs, or Splitbacks (also called Wingbacks or Halfbacks) are usually recruited RBs with enough speed to get around the corner on a sweep/end-around and yet still catch a pass over the middle. There's nothing mystical or gimmicky about it, Johnson just puts people in a position to win with sound principles. Has misdirection been abandoned in pass-happy offenses? Do we not ever use lead blockers or run traps and counter plays in a spread? What about double-teaming DL and LBs on a HB power play?
But how does one defend against any option team, particularly the Flex? If the opponent has a smart coach like Johnson, you're doing well to hold them under 4.0 per carry, because he knows how to make adjustments to what you're showing them. However, there are basic tenets to stopping the triple-option and Wing-T/Flex that we can go through.
-Take away something: The Dive or the Pitch, but preferably the Dive.
-Control the LOS: You must control the operating space of the QB and dive backs in the middle.
-Get the LBs into the running lanes: The DTs cannot be knocked backwards and the LBs must fill the lanes and be free to move.
-Discipline: Defenders must know how to recognize blocking schemes, and not worry about his teammate's job, only his.
-Lack of Stunting. You dont want to get caught in alot of stunts or play too many tricks up front, because you'll just open a hole for a Dive.
Of all those things, the most important is stopping the FB Dive, it sets up the entire option offense, no matter whether you use a Flex or a Wishbone or the "I" formation.
The key to defending the veer here is the dive...if the DE gets sucked in or if your DT's lose ground, you may as well pack your shit up and go home, cause you are going to give up 10 yards. Its a direct-attack play that forces your DL get off their blocks, and the LB/S to choose whether to come up and make a play or wait for the pitch. In a true option, the QB has a choice on every play whether to run the Dive, by watching the defensive end. If he sees the End stand pat, he gives the Dive. If the End collapses inside, the QB takes it himself around the corner with a pitch man behind him.
What is missed when people talk about the Bone is the play of the interior linemen. The Dive is all set up from the Center and Guard play. Generally they will be doing the same thing. If the Center blocks down, so will the Guards (but one might pull for the Trap). If he charges upfield to take out Mike, the Guard will try to follow. If Mike is knocked out of the play by a block, you can expect to get a minimum of 4 a carry.
If you bring everyone into the box, to stop the interior rush, then you are setup for the Keep:
Its relatively simple in concept, but the GT offense uses misdirection and motion to confuse the secondary and LBs, less so than an I-formation offense that would normally run directly at you with more lead-blocking plays. If one S/OLB's key is the splitback/wingback to his side, then when he runs across the LOS, he must immediately go to his next key or follow. Also with everyone up in the box, you are setup for the pitch play:
In the pitch play above, you see the Miami safety was keyed on the Wing, and cheated closer and closer, and once he broke to the other side, he had to follow because he was the only key once the safety read run, but he was so close that he got blocked out when he crossed midfield. The LBs, worried about the Dive play, all came up to stop it, but the QB keeps the ball and reads the OLB.
Since the DE had come inside (one of his keys is still the OT/TE) to stop the Dive, the OLB was out there alone, with his normal assignment being the pitch man and not the QB. He turns inwards and blocks the alley for the QB, forcing the pitch, except that the CB has been knocked out by the WR and the play gains 40yds.
So how do you teach a defense to stop this kind of offense? Primarily it comes down to discipline and good fundamental defense, with the key player being the DE. A good defense may simply have so much speed that they are always near the ball pretty quickly, and they tackle well enough so that they make plays. That doesn't mean the players are always in the correct positions, just that they manage to recover quicker than the offensive back can take advantage of it, and they swarm to the ball to make up for any bad tackling. The Flex is different from the Wishbone mainly in that it has those two TE/WB players (who may just be RBs that can catch) set outside, but the coverages run against both are usually Cover 1 Man or rotated zone because you still must keep enough players close to the LOS.
Something that many people do not realize about teams that run this offense is that it is very confusing to figure out who has the ball. You begin each play with three running backs and a QB. There is often a great deal of motion, with players "criss-crossing" in the middle of plays (this constant motion and excessive number of ball handlers makes a a defense that is not fundamentally sound easily susceptible to any sort of counter play--specifically an inside handoff).
Here is a basic rundown of what most coaches will teach in defending the Flex, or any other triple option offense. It is primarily the same run keys (and sky/cloud calls) for any defensive back, so their specific assignment duties wouldn't change much week-to-week from a pro-style team to an option, except that they may be told to cheat up more than usual.
The DE is critical here with the veer to maintain containment on the fullback while acting as the "force" man should the QB fake the dive. The End must be more athletic than the man in front of him to slow down the veer, be thankful we have D. Bowers and Ricky Sapp. The End must be the force, making the QB take more time than he wishes and most importantly make him pitch the ball.
Against the double-wingback set the End has a difficult assignment, but its best to play either an anchor or loop technique to keep it simple. The Ends are primarily responsible for forcing the Pitch. They play for time, and wait for help from the inside, because the option will force them to make a choice on who to tackle. They must be aggressive. Against a veer/pitch play, the End gets his inside hip into the hole and rotates his feet towards the sidelines, and doesnt jump on the dive back unless he's coming directly to him with the ball.
On the snap, using the Anchor, he'll charge the TE to give him a shiver, helping the LB thats scraping across behind him. All the while he's keying the FB first, and if he goes away or up the middle, he backs upfield waiting for a counter sweep or a bootleg. He has to do this even if the Wing is trying to block him. If the FB comes toward the end, he flattens out to prepare for his block (on a power sweep play, or the Guard's block on the belly play) but keeps his feet parallel to the line.
If he's playing a Loop, after the snap he charges upfield in the TE/WB seam and reacts the same way to the FB key as before. If they try a bootleg, he's supposed to be there waiting.
Against an arc play, where the TE across him will try to come upfield and block the SS, he has to stand pat with his outside foot back. He has to feel for his help, and then come down the line to make the play. Against a Load play, where the Dive back will come off-tackle or off TE (the TE/WB will usually block inside), the End attacks the load blocker and forces the QB to go around him, then tries to get off the block and make a play.
Tackles key the Diveback and the QB. They must be taught to get off blocks and not be moved from the LOS, and simply be aggressive against anything they see.
You want to keep the LBs within 4 yards of the ball, so that they can read on the move and react effectively. Because of the misdirection, LBs have a hard time keying one back or the ball, which is why this offense is difficult to defend. Instead, they are told to key the Guards and react from that.
If the G blocks inside on the NT over the Center, the LB has to step in to the OT for the trap play, keeping his outside arm on him. If the Guard base blocks (i.e., straight up on the DT across from him), the LB looks for the ball and plays an assigned gap (usually A/B). If the flow of the play is away, they are taught to rip through the Guard's block with their outside forearm, aiming for the A-gap on the opposite side. If the Guard pulls, the near LB pull with him.
You will either see more Cover 1 or a rotated cover 3 zone against this offensive scheme, and this (rotated zone) is what Clemson primarily used last year in Death Valley. This year I expect GT to use more misdirection and pass a bit more because more teams will stack the box against them after what they did to Miami last season. Whether Kevin Steele will use more zone against GT or stick to his Cover 1, I'm not sure. Like I said, the Corners are usually out wide because the slot man is not on the field between the Wing/TE and the Flanker in the Flex, so they can be on an island by themselves.
In a rotated coverage, the secondary might key the FB to determine the rotation. This would help them cover the counter pass, or a fake keeper pass. As the two safeties rotate, they read the blocks of the Wing for run, and if they ever show blocking for a counter, they stop rotating and play run support. Otherwise, the secondary keys the ball, which places the responsibility of the counter pass on the OLBs.
Finally, the defense cannot be lulled to sleep. A good offense can run simple plays like the dive, toss sweep, iso, and off-tackle all afternoon and can do this with relatively little motion (often shifting a wing to a split back or i-formation look). If you were watching the Clemson-GT game last year, you saw them consistently get 3.5-4 per carry against us, and by simply running the same play over and over again. It only takes 3 runs of 3.3x yards to get a 1st. Methodical operation of this offense has a tendency to get the defense complacent and lackadaisical, allowing the offense to run a misdirection play or for the QB to pull the ball on what looks like a FB dive. Defensive inattention allows the offense to go from 3-4 yds repeatedly with the dive, iso, or offtackle rushing play to picking up a huge chunk of yardage because defenders are out of position and anticipate the 3-4 yd play.
An addendum, for the R&S concepts from the flexbone, is here.