The back judge is an official in the NFL who is positioned in the deep backfield on the tight end's side of the field. He is one of seven officials present throughout each game. The back judge focuses primarily on the tight end and his movements, but he has other responsibilities, too.
The back judge is responsible to observe and make calls for the following:
The back judge covers the field that is between him and the umpire, which is a wide part of the middle field.
The back judge is mostly responsible for the tight end, and ensuring that any defensive penalties or illegal blocking is called. He is the official who will determine which team is awarded the ball after a fumble and makes calls on legal catches. When it comes to delay of game calls, the back judge is in charge of making those calls when it comes to the game clock.
PRO TIP: Did you know that the back judge has the final say on whether or not a kick is legal?