An ineligible downfield pass, also called ineligible receiver downfield, is a penalty in Football that is called on the offensive team when a forward pass is completed to an ineligible downfield receiver. An ineligible downfield receiver is any player who did not line up off of the line of scrimmage, such as the offensive guards and tackles. This results in a 5 yard penalty against the offense.
This penalty is in place to prevent too many players from being eligible receivers. If an ineligible receiver were to catch a pass, how could the defense possibly defend a player who is not even supposed to be a receiver?