Why do offensive linemen point at defense during snap count?

Answer 1

In the NFL blocking is often determined by the defensive player positioning. Usually the center comes to the line and points and calls out the blocking assignments. Sometimes the quarterback may see a situation he recognizes and assigns someone to block a player he thinks is going to try to tackle him before he can pass the ball or he recognizes the player is filling the gap where they intended to run the ball and assigns aplayer to block him.

Answer 2

They're identifying the middle linebacker (AKA the Mike linebacker or MLB). Most offensive lines use a numbering scheme that begins with the MLB. Since the MLB will align differently against various offensive formations, the offensive linemen seek to point him out, so they know where the numbering system begins and what everyone else's numbers are. It also helps the running backs identify the blitz easier, since, in certain protection schemes, the running back will be responsible for picking up the MLB coming up the middle on what's called an A-gap blitz.

Answer 3

The lines of a football playing field tell the players the number of yards they are on. In addition, the lines at the end of the field are called end lines. The lines along the side of each field are called side lines.