An illegal peel back is a penalty in Football that is called on a team when a player performs a peel back block. A peel back block is a block in which a player blocks an opposing player who is running towards their own endzone from the side and below the waist. A peel back block is also commonly referred to as a crackback block. This penalty results in a 15-yard loss for the offending team.
Peel back blocks outside the tackle box have been banned since 2005, but were recently banned inside the tackle box since 2013. The block is banned due to the injury risk and the player being blocked unable to defend himself.