This article covers what is about perhaps the most widely used run play in all of football... the inside zone run (the only competitor in my mind is the draw). One of the main reasons it is run so often is that it is simple and modular. With a relatively small collection of tags, an offensive coordinator can turn inside zone into half a dozen or more plays. Everything from mid-line option to ISO runs are possible within the framework of this one blocking scheme if a team is able and willing to invest enough time into it.
Let’s start with the basic idea behind inside zone. To begin, every offensive lineman takes a step toward the play-side and about 45 degrees forward. The linemen do not step straight forward because they are responsible for the gap on the side to which the run is designed to go. To keep things simple, we'll focus on inside zone right. Each lineman controls his gap, blocking whoever shows up there. Most of the time, the right tackle takes on the end, the right guard takes on the linebacker, the center takes on the one technique etc., unless one of the players moves after the snap. If a player moves out of a gap after the snap, the lineman simply takes whoever fills that gap. If no one fills the gap, then gap will be open, and any running back worth his cleats will turn that into a nice gain.
No team actually runs inside zone like this, though, mainly because it sacrifices one of the biggest strengths of the play - the potential for one or more combo blocks, pushing a defensive lineman off the ball. The team that pushes the other team off the ball tends to win. If there is a defensive lineman (linebackers on the LOS are counted as DL) in the OL's gap, the OL blocks as designed. If a defensive lineman is not in the OL's gap, and there is one in the OL's backside gap, then the OL will start the play by stepping opposite the playcall. Both linemen, the one blocking his usual gap and the one blocking his backside, will then converge on the defensive lineman and try to drive him as far as they can. Both linemen must also keep their heads up so that when the time comes, one lineman can disengage and block the linebacker. The offensive lineman who began the play by stepping opposite the playcall will almost always take the linebacker. If the linebacker blitzes after the snap, the double team is off. If the defensive lineman moves to where only one of the linemen can get to him, the double team is off. The rule for which OL takes the DL boils down to "do not let anyone cross your face." The two things that beat inside zone are penetration and linemen who cannot find a linebacker at the second level.
The running back's job in inside zone is pretty simple: get the ball, wait for the play to develop, find a hole between the guards, and run like mad. Running backs in this scheme are allowed to make one cut behind the line. They are expected to be patient, but decisive. If the running back cannot do this, the running back is probably getting pulled from the game and cursed out by a few coaches, including the OL coach. You do not want to be cursed out by an offensive line coach. The goal of inside zone is to consistently carve out four to five yard chunks from a defense. If a back cannot do that, the back will not get the ball. This play is not meant to be a home run hitter. It is the jab. It probably won’t yield a knockout, but the blows will add up over time and will open up the knockout punches.
Let’s go to our first tag, a tag that’s probably familiar to everyone reading this, the zone read. As you probably noticed above, the defensive end away from the playcall is not blocked. There are multiple ways to deal with this. The zone read deals with it by enabling the quarterback to read the end. If the defensive end crashes down to try to stop the running back, the quarterback can pull the ball and get some yards. If the defensive end sits at home, the quarterback has effectively blocked him, and the offense can go on bludgeoning the defensive front.
Our next tag is a spin-off of the zone read, the mid-line option. This play requires a bit of thinking on the offensive lines part. The tackle to the read side will be blocking the end on his side, and stepping with the opposite foot as the rest of the OL. The guard to the read side has to avoid the defensive linemen and go block a linebacker instead. Everyone not on the read side will run inside zone as usual. The running back will as well, though he has to be more careful about cutbacks to the weak side. The quarterback, instead of reading the defensive end (who at this point likely has extensive coaching on how to handle the zone read), will instead read the defensive tackle (who may not). In addition to changing the read key, mid-line runs allow the quarterback to hit the line of scrimmage quicker, albeit in a more congested area of the field, making it a good play for short yardage situations.
Following midline is the brick tag, wherein the backside tackle blocks the backside end, the backside guard will take a tackle, and the backside inside linebacker will not be blocked. If there are only five defenders in the box, this inside zone is run like an old-man-blocked dive play. If there are six in the box, the quarterback must read the unblocked linebacker, either keeping the ball or throwing a stick route in the area the linebacker vacated.
Now let’s really escalate things and introduce a fullback/tight end type to the equation. I will call him a fullback from here on out because I like fullbacks. Our first tag here is solid. The offensive line and running back runs the inside zone as usual. The difference is the fullback will block the usually-unblocked defensive end. Usually the fullback will just cut the end, but every so often the end will not see the fullback coming and get blown the whole heck up. This frees up the quarterback from having to possibly run the ball (and risk injury) as well as letting the running back know no unblocked player is going to tee off on him if he cuts back. In addition, if the quarterback is not reading the defensive end, he can have his eyes elsewhere, making post snap reads on a bubble screen or some other quick pass packaged with a run play. Not that that can’t be done while running an option, it’s just easier this way.
A spin off of the solid tag is the slice tag. Everyone operates just like they're running solid except the fullback ignores the defensive end and loops around to block a force defender. The quarterback reads the end just like a zone read, except now, if he pulls, he has the fullback acting as his escort. As a bonus, the defensive end will often freeze, bracing for an impact that never comes. The running back tends to run the ball more in this variety of zone read, but the quarterback keeps will tend to be more explosive.
I have a theory that because so many offensive coordinators were quarterbacks and as such got hit by defensive lineman a lot, offensive schemes focus on making defensive linemen’s lives difficult. When a defensive tackle is unblocked, usually the warning light goes on, and he is aware that he is either being screened, read, or trapped. In two of those three situations, the defensive lineman is supposed to sit still near the line of scrimmage and look for the ball. Unfortunately if the lineman is being trapped, sitting still will get him blindsided by a large angry man with a head start. If the defensive tackle runs like crazy upfield he will also be blindsided, just at a different angle. If the defensive tackle recognizes a trap play fast enough and engages the blocker, he is still being hit by a large man with a head start but he at least knows it’s coming. Usually the end result is a large hole for the running back to run through. The wham tag enables teams to run trap plays without installing a new blocking scheme. The offensive line blocks everything like a mid-line, and the fullback serves the role of the large angry man screwing up a defensive tackles day just because he can. It is a mean, mean play that Arkansas runs a lot, and I love it.
Finally, let’s see what a fullback can add to the brick tag. If an offensive coordinator wants to run ISO he can tag, well, ISO. The fullback will take on the linebacker unblocked by the offensive linemen. The running back will read the play as normal, and the quarterback is free to either run a play fake or read for a quick throw.
But let’s say you’re trying to be mean to linebackers too, because why not? Well, Kansas State had a nifty little package play last year where the fullback runs up like he is attempting to ISO block the linebacker. The linebacker does what instinct, position coaches yelling his entire life, and pain have taught him to do. He runs up to meet the fullback in the hole. Only the fullback runs right past the linebacker, turns around, and the quarterback throws an easy pass into his hands.
As you can see, there’s a lot you can do with inside zone, and you only have to teach your offensive lineman one blocking scheme and two tags. There's no need for them to know what the fullback or the quarterback or the slot is doing. With a handful of creative tags, motions, and good game planning, an offense can get a lot of mileage out of a simple scheme. There's no reason a team can't call QB ISO, then follow it with a stick route to the slot, then come back with a running back dive, all within one blocking scheme. It’s really only limited by how creative, mean, and invested in the scheme your offensive coaches are.