I’ve been watching football forever, but I still don’t know the answer to these questions:
How can you tell, at a glance, whether a defense is playing zone or man defense?
What is the quarterback signaling when he slaps his helmet? When he lifts one leg?
mmm
You can’t, always. That’s why to offense will sometimes put a man in motion to see if a defender follows him. If so, they’re likely in man coverage. Defenses can disguise thier coverage schemes, so it’s not a foolproof test.
The QB can signal a bunch of things, but it’s often “Pay attention, I’m about to signal something important.” It’s also helpful for timing when things are really loud in an opposing stadium.
Generally (but not always, of course), if the cornerbacks are up close to the wide receivers and facing them, it’s man-to-man. If the corners are a few yards back and watching the quarterback, it’s probably zone.
This could mean any number of things, but I think that the leg-lifting often is a signal for another offensive player to start going in motion. A slap of the helmet may mean that he’s changing the play based on the defensive alignment. Or not.
This one is fairly straight-forward and universal. In a loud stadium it’s hard for the offense to hear the QB’s voice when he’s in a shotgun. They shift to a silent count, which essentially means that the Center snaps the ball without waiting for the QB to shout “hike”. Before the Center does that, he waits for the QB to signal that he’s done making adjustments and is ready to receive the ball. This is what the leg lift signal means. The Center is watching between his legs to see if the QB lifts his leg. When he sees that he lifts his head to take a final look at the defense himself and snaps the ball when he’s ready.
In some cases the leg lift can also be a signal to a WR to go into motion but that’s a less common these days.
Highly variable. And teams know that the defense is watching so they don’t want this signal’s meaning to be too obvious or predictable. There’s a decent chance that the QB used it to mean different things at different times and they will change the signal’s meaning based on situation or opponent. They aso might do it and have it mean nothing as a distraction. Like the leg lift it’s another silent signal used to combat crowd noise.
When a QB wants to audible to a different play based on the defense’s alignment he needs to tell the team that they are changing plays. At home in a quieter setting, they’ll use code words which gives you a lot of flexibility in communication. On the road when it’s loud they need to use non-verbal signals which are simpler. Tapping a helmet is a common tactic to signal that, but there’s any number of other hand signals they might use. QBs sometimes will use it to communicate one specific message to a veteran WR if he sees something and they are going to freelance a little. Aaron Rodgers did this a lot with Davante Adams. This wasn’t technically an audible, but still sent a message to do soemthing other than what the play in the huddle was.
Exactly. This is part of the chess game that is American Football. The QB tries to guess what the defense is doing based on their formation, and then revise that guess in seconds or less than a second based on how they move after the snap, but it’s still going to be a guess.
And in some plays, you wonder if the defense knew whether they were supposed to be doing man or zone coverage… 
As others have noted, this is a huge element of the game. It’s a cat and mouse game. The entire offense, not just the QB, is trying to diagnose the defense’s plan both before and during a play. If the offense knows what the defense is trying to do they have a huge advantage, and any competent offense will be highly successful if the defense is unable to disguise a coverage.
There are certain situations where only one scheme makes sense and both teams know it. These are somewhat rare, but it happens. For 95% of plays the defense is trying to hide their coverage up until the last possible second and the QB is trying to use motion and cadence to get the defense to show it’s hand early. Or else they try to move very fast so that they can use the defense’s disguise against it because players are slightly out of position.
The differences are subtle. If a defender has one foot forward versus the other, or his hips shifted one way or another, that could signal a type of coverage. If the defender is looking at the receiver or at the QB could signal it. If they are closer to the line of scrimmage or further back it could signal something. What personnel in on the field can be an obvious indicator as well. But the defense knows all these cues so they will try to hide their intentions or show one subtle cue as a decoy. Good QBs can spot the differences. Good offensive designs use formation and motion to make it harder to hide coverages. It’s hard to overstate how central this is to the game.
But, once a play has begun, the coverage gets revealed. Even an amateur like me can recognize a coverage after the snap. Man coverage is easy to spot. Deep zones are easy to spot. Underneath zones and handoffs add a little complexity but still, at this point the defense is no longer trying to conceal anything. They just need to do their assignment for the 3-5 seconds it takes to run the play.
If I may run a side route on MMM’s question here:
I’m not sure I have a complete understanding of what situations call for zone vs. man offense.
What I think is, if a defense wants to, say, run a blitz, or if they think the offensive formation is reading ‘rush play’ they may keep an extra man up front and do a zone defense as a ‘backup’ just in case the blitz fails, or the assumed rush play turns into a pass. Also, if a team’s defense does not have particularly fast or talented safeties they may more often resort to a zone defense.
But if an offense has a strong front line so it’s tough to collapse the pocket, or if the QB is a quick-throwing, accurate and prolific passer, like a Brady; or if the defense does have fast, talented safeties, then they would more often go for a man defense.
Both those scenarios assume that a man defense is always best against the pass, but are there gaps in my understanding? Are there situations where a zone defense is better sometimes, even on passing plays?
Many teams play zone defense in the Red Zone, because there is less field to cover.
But if a team is blitzing the QB, then man defense is better.
It’s worth mentioning that teams typically don’t run a true “zone” or “man” defense on a given play. Most defensive plays use a combination of zone and man concepts. Even in a true zone play call, some defenders are told to shift to man when the receiver does a specific thing.
In one extreme there’s a Zero Blitz or Cover 0. The zero in zero blitz means that there are no men covering the deep zone. Everyone is either rushing the passer are manned up against a receiver. In extreme cases you might even have uncovered men, but that’s typically a recipe for disaster. This is the closest you’re likely to find to a pure man-to-man scheme. Almost every other call has at least one player playing zone.
Cover 1 means you have one safety back covering the deep zone. So in this play there’s at least one guy playing zone. The rest of the guys might be playing some combination of zone or man depending on the flavor of the coverage.
Cover 2 predictably has both safeties each covering half the field. Again, you have 2 guys in a deep zone scheme, the remainder can be playing a combination of zone and man.
Cover 3 adds a third player to the deep zone, splitting the field in the thirds and each assigned the deepest parts of the field. This is obviously a softer coverage, used more on obvious passing downs. The 3rd guy is usually a nickelback or one of the cornerbacks but in some modifications can be a LB.
Cover 4 extends the idea to the extreme where you split the fields into 4 parts and drop all 4 DBs into a zone coverage. At this point you usually don’t have any DBs left for man coverage, but you could be using a LB to man up on an RB out of the backfield.
Cover 6 sometimes is used to describe a combination of a Cover 2 and Cover 4. You’re basically splitting the field in half and playing Cover 2 on one side and Cover 4 on the other side. So one side will usually have one DB manned up on a WR and the other side will be running a pure zone.
There are infinite variations on each of these, but the primary point is that in almost every situation you’re going to have someone in zone. Man coverage is a more aggressive posture. Even when you are playing man on a receiver you provide a second line of defense with a zone defender over the top.
Wanted to expand on this specific point a little more. Short answer, no, one is not “better” against the pass than the other. As I mentioned above, man is more aggressive than zone. Aggressiveness is useful when the situation calls for it, it can be a liability otherwise.
Football is a numbers game. With pass blocking, you want to have more blockers than rushers. You also have the QB throwing the ball. Commonly this means you, the defense, have 7 guys to cover 5 potential receivers. You have an advantage and zone is the conservative way to use that advantage. The offense needs to be great to win on that play. Even a catch is unlikely to go for big yards. But sometimes the offense wins so you as the defense need to be more aggressive, you can play man mixed with zone to increase the degree of difficulty (but also increasing the risk of a big play). You can also play man mixed with a blitz to increase the degree of difficulty, with even more risk. It’s all a series of tradeoffs.
Makes sense that a defense would play zone in a short-field red zone situation. Thanks.
Thanks for the in-depth explanation, Omniscient. Good stuff!
Like Telemark said, defenses try to disguise what they are doing as much as possible. Sometimes they play a hybrid zone/man defense. Sometimes they blitz but drop a lineman into the vacated area hoping the quarterback will bite and throw the ball there. It’s a constant chess game. Experienced and talented quarterbacks are hard to fool. They read defenses very well.