What Is Illegal Substitution In Football?

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What Is Illegal Substitution? 

Illegal substitution occurs when a team puts too many or too few players on the field during a play. This usually happens because of confusion between coaches, players, or officials as to where they should be lining up on the field.

It can also occur due to one team trying to gain an advantage by sneaking an extra player onto the field without being detected. Regardless of how it happens, this infraction is illegal and will be called if noticed by game officials. 

Examples Of Illegal Substitution

1. Entering the field of play without first being announced by the referee

2. Trying to enter the game after the play has already started

3. Not entering the game at the proper time during a change of possession

4. Lining up in an illegal formation

Why Does It Matter? 

Illegal substitution carries with it several consequences for teams that commit the infraction. A team guilty of illegal substitution may be penalized for five yards per infraction. These penalties are designed to keep teams honest and prevent them from taking unfair advantage by having extra players on the field who could interfere with opposing players or plays. 

When Does It Occur? 

Illegal substitution typically occurs before or after a play has been put into motion; this usually occurs when substitutions are made between offensive or defensive sets or when special team personnel enters and exit the field while play is ongoing.

To avoid these costly penalties, teams must make sure that everyone entering and exiting the field does so properly—that means ensuring everyone knows where they need to be lined up ahead of time so there is no confusion once play begins.    


Illegal substitution is an infraction in American football that carries serious consequences for teams guilty of committing it. Not only can teams lose yardage due to penalty flags, but they can also lose possession altogether if too many players from one side are on the field during a given play.

To prevent these costly errors from occurring, coaches must make sure their players know exactly where they should be lining up before each snap, so there is no chance for confusion once play begins. Doing this will help ensure your team stays out of trouble and avoid unnecessary penalties down the line!