A term for any infraction that occurs while the ball is in play. A live ball foul is signalled by the official throwing a flag, and the penalty is announced following the conclusion of the play. The effect of a live ball foul differs depending on the specific infraction, but in most cases the team against which the infraction was committed will have the option to take the result of the play or have the down replayed with a yardage penalty.
Live ball fouls allow the play to continue, and the penalty is determined at the conclusion of the play. In most cases, the team that was not penalized will have the option to take the result of the play, or have the down replayed with a yardage penalty against the offending team. This is different than dead ball fouls because the yardage is tacked immediately on a dead ball foul. In the event that both teams commit a live ball foul, the down is automatically replayed.