An illegal forward pass is a penalty in Football that is called on the offensive teams when a second forward pass occurs following a forward pass or when a forward pass occurs after the passer has crossed the line of scrimmage. This penalty results in a 5 yard loss from the spot of the foul and a loss of down.
Illegal forward passes can also occur during what appear to be laterals or backward passes. For a pass to be considered backward, the ball must land or be caught behind the yard line from which it was tossed. So if a quarterback tosses the ball from his own 30 yard line and it is caught at the 29, it is a backward pass. In a game against the Philadelphia Eagles in 2017, Russell Wilson committed an illegal forward pass that appeared to be a legal lateral.