Linebackers and Defensive Backs can read the keys of offensive linemen to learn the direction of the play.
1. Offensive linemen blocking down field means the play is a run.
2. Offensive linemen pulling in one direction generally means play is in direction of pull.
3. Offensive linemen drop stepping and setting up to block for pass protection means pass but also could be a draw or screen.
When reading your keys don’t get too excited and in a hurry and move to quickly. Be patient. A move in the wrong direction takes time to recover from.
LBs and DBs should take a small drop step with either foot while reading their keys. You first move should not be towards the line of scrimmage.
From Bud Wilkinson’s Football Winning Defense
Play for Fun and Winning is Funner.