An NFL question:

[Ptah]

Just before the snap, offensive linemen gesture or point to someone or somewhere on the defense.
Are they saying "Imma knock you out"?

[House of Roberts]

1. It's a way of locating the middle linebacker or another key defender,

especially if he lines up in a slot that might prevent the play from succeeding.

[walkingman]

2. Exactly as House of Roberts says, the center or even the QB sometimes will identify the "Mike" (middle lb)

by saying his number during his cadence so the OL can know who's responsibility it is to block him. In some of the defensive schemes, they do not use a MLB.

[marble falls]

3. Or asking the player opposite if they want some "nekid pichers of yore waf." They also might be reading the defensive ..

... line for hints of whether it's going to be a blitz, trying to figure out where the defense is going to hit.