Then educate me, please. I don't watch football, so I'm sure I'm missing something.
Offense: Motion
One or more players can move to a different position, which potentially changes defensive coverage assignments or requirements
Snap count
The timing of when the ball snaps changes depending on what the QB wants each play. This is used to keep the defense from knowing exactly when the play starts.
Also, a hard count is often used to make defenders jump offsides in crucial situations. If successful, it can change the outcome of the game in certain situations.
Hot routes
QB reads the defensive coverage before the play and may tell a receiver to run a different route based on that.
Audibles
QB tells the offense to change to an entirely different play, and can sometimes even change the formation entirely before the snap.
Defense: MLB reads the QB
Even with a planned defensive play in mind for the group as a whole, the middle linebacker can tell the defense what to do on the fly. Depending on what he thinks the QB is doing in the items mentioned above, he may change the coverage types or change the defensive play altogether.
Coverage/Blitz show/fake
Show a blitz: This is when a defender creeps toward the line of scrimmage to reduce the amount of time it takes for him to get to the backfield if he's blitzing
Fake a blitz: This is when a defender creeps toward the line of scrimmage as if he's blitzing, but then drops back into coverage when the play starts. If the QB falls for this, he may make a bad throw and possibly an interception.
Blitz disguise: A defender may pretend to be assigned to cover an offensive player pre-snap, but blitz once the ball is snapped.
Coverage disguise: Players in man-to-man coverage will typically line up right in front of the player they're assigned to defend against and keep their eyes on the player. Man-to-man coverage means the defender tries to stick with his assigned offensive player through the course of the play. Players in zone coverage will typically give a cushion between themselves and the defender and only defend a certain area of the field. In zone coverage, a defender may be responsible for defending against multiple offensive players, depending on where the offensive players move to on the field during the play. A disguised coverage is when the defense either makes their formation/actions look like they're going to be in man-to-man or zone, but they're actually going to switch to the opposite coverage type during the play. If the QB reads wrong pre-snap, this can result in a bad throw or interception. Defenses can also try to disguise whether they're in cover 2, 3, or 4 by their formation in order to make the QB think a certain area of the field will typically be safe to throw into when it isn't.
