Any time a pass attempt is caught by an eligible offensive player. Passes are completed when the offensive player has gained possession of the ball by securing it with his hands or body and placed two feet down in the field of the play. For the completion to be valid, the ball may not touch the ground prior to being secured. After a completion, the player with the ball may advance down the field of play until tackled or running out of bounds. Passes are most likely to be completed to wide receivers, although tight ends and running backs are also eligible receivers. Pass completions are recorded only for players who attempted the pass; the act of catching the ball is called a "reception".
Pass completions are a main aspect of a successful offense, as effective quarterbacks will complete a higher percentage of their pass attempts. Completions can occur anywhere in front of the quarterback and generally occur more often when the receiver is open. An offense will tend to attempt passes at various distances, so the yardage gained on a completed pass can vary a great deal. A good completion will leave the receiver in a position to run after the catch, gaining more yards for the offense.