An illegal substitution is a penalty in Football that is called on a team when an illegal substitution occurs. An illegal substitution occurs when at any point during the offensive huddle, a team has more than 11 players in the huddle at any point, from the formation of the huddle to the break. An illegal substitution can occur on defense if the defense has more than 11 players on the field at the time of or simultaneously as the snap. This penalty is concurrent with the too many men on the field penalty. This penalty results in a 5 yard loss for the offending team.