College football referee mechanics

Question
Which official on the college football field is responsible for determining if the QB has passed the line of scrimmage on a pass?

Answer
Doug
In 7 man mechanics, the Line Judge - LJ will be on the line of scrimmage and he will look down the line to rule whether the passers  crosses the line; however, the Referee has responsibility for the QB so he will follow behind and look to see if the pass was thrown behind or beyond the line of scrimmage.  Whenthe crew is in Goal line mechanics [from the 5 yard line and in] the umpire will come up tot he line of scrimmage and help out determining if the passer throws the ball from behind or beyond the line of scrimmage.