Indiana heavily utilizes the screen game to act like a rushing attack. In fact, a lot of their success comes off of screen misdirection and screen action, both things that are commonly associated with the run game. By doing this, they create conditions exactly what the spread offenses was designed for: to stretch offenses laterally as well as vertically. For defenses, this means a couple things, they must be extremely disciplined with their eyes and they must tackle in space.
Brief Screen Primer
A brief background on screen blocking first. The lineman that release depend on who isn’t covered and which defenders present a risk to the ball in the air or the receiver. This means any defender that will try to get in an alley between the passer and receiver must be cut down or washed away. Preferably on any outside screen you’ll have at least one blocker sealing off the inside to outside pursuit, another acting as a lead blocker in the alley, and another acting as a support blocker, which basically keeps any outside defender outside and then works upfield as an extra lead blocker. Typically, Indiana leaked the playside guard to be the support blocker and the center to be the lead blocker and a receiver to be the sealer, so for simplicity and consistency, I’ll draw up the plays like that.
A flare screen is a quick screen to the RB that acts almost like a sweep play but allows the RB to start a little more lateral. It isn’t set up to suck defenders in as much on the pass as it is intended to make them hesitate for a brief moment so that blockers can get out on them and the RB can work in space. The reason to run a flare screen rather than a simple sweep is because, with the flare screen, you are hoping to get outside the initial leverage defender. Backside OL will reach block and work to the second level to hold everything inside.
This is usually shut down either by an OLB correctly reading the playside guard and beating his block into the flat, or more often by a flat defender coming off his man and meeting the RB in the backfield before the support blocker can get out on him.
Bubble Screen (Swing Screen)
The bubble screen attacks the edge of the defense by out flanking them (because of that, the blocking assignments don't contain the typical support, alley, and seal blockers). This can often be combined in a package play with a zone run, but when not, the OL will execute and outside zone blocking scheme toward the bubble action to again try to seal the box defenders inside. The receivers will block the person stacked over top of them with the idea that, by blocking them, the defender covering the bubble receiver will get caught in the wash.
This is usually defended by the outside CB winning at the point of attack and controlling the WR at the LOS. By not letting the play get outside of him, he forces the ball carrier to hesitate and go back inside, where support is coming from.
Tunnel Screen (Jailbreak/Alley Screen)
The tunnel screen is designed to attack the natural tunnel or alley that forms between the box defenders and the defensive backs covering the receivers. As usual, the OL will outside zone block in this case. Either a RB, a playside TE, or a playside OT will be responsible to be the lead alley blocker. The receiver inside of the receiver eventually catching the ball will be the support blocker, blocking the man covering the eventual ball carrier. Either a #3 receiver, a RB coming around the formation, or the OL will be responsible for sealing the defense inside the box.
This screen is usually blown up one of two ways. First, by the outside CB cutting underneath the support block and staying right on the butt of the intended receiver. Second, by the leverage defender playside reacting to the look and squeezing the alley before blockers can reach him.
Traditional Screen (Slow Screen)
This is your traditional RB screen. It tasks the OL with sucking the defense up the field. The OT will continue to drive his DE up the field so that the player can’t make a play on the ball in the air or disrupt the receiver. The playside guard becomes the support blocker, the center is the lead blocker. The receivers will typically be the sealing blockers, and the backside guard may try to flip and seal the pursuit defenders from making a play, also known as a peel blocker.
This play typically gets blown up by the DL reacting to the OL release or by a LB cutting underneath a block and making a play on the RB.
The first two screen plays I described are considered quick developing screens, while the second two are considered slow developing screens. Any set of quick and slow developing screen can be combined to utilize misdirection in the screen game and provide the offense with multiple options. Indiana does this a lot.
Here, the QB’s first read is the quick screen rush end. If he quickly crashes, the QB can hit the flare screen, if he hesitates, holds up, or peels, the QB can pump fake, continue to drift, and hit the slow screen side. For the slow screen portion, the screen misdirection acts as the "seal blocker".
This means that a defense must read their keys correctly. Trying to play outside your assignment will get you caught out of position and the offense will take advantage.
You can also see how a bubble screen and tunnel screen work in combination.
And in fact, you can run a quick tunnel screen and run two tunnel screens as well if you so desire.
For every type of screen play, there is a screen action that goes along with it. Indiana will utilize this when defenses start playing aggressive and lose their initial assignment in the pass game.
For example, here’s a flare action pass. The seal blocker will stop in the hook zone, someone else will run a seam, and the RB will convert his flare into a wheel route.
And bubble action, where the blockers will run vertical routes to pick on the deep safety whom doesn’t have help from his CB.
Or tunnel action, where the support blocker will convert into a wheel route, another receiver will run a seam, and the initial screen receiver will convert into a delayed slant and sit in an opening in the defense (against zone) or continue on the slant against man coverage.
All these things stress a defense to play sound and not over react to what is going on in front of this. This is difficult, because these screen plays are getting people open in space, and the key to a defense is always to tackle in space, which means to get at least four defenders in a position to tackle the football. But if you leave your assignment early you can be beat over the top by the screen action or by misdirection. So there is a fine line between swarming to the football and staying within your assignment, and that very fine balance is what gives this offense the advantage most of the time.