illegal defence subsitution

[pioneerstats]

what is this call and can it happen on change of posesion. at a game the other night team stoped near goal line on 4 down
other team takes the ball and before the snap gets 5 yards on illegal defence subsitution gets them out of the end zone

 

[White hat]

I'm not exactly sure what you are saying was called, but yes, there can be an illegal substitution on the defense. If 12 players are out on the field and no one appears to be leaving when the offense is ready, then it's illegal substition on the defense. Officials try to blow this play dead and penalize the 5 yards before the snap because if the play starts and 12 are on the field, the penalty is 15 yards.