[The Roamin' Umpire]

The NF mechanics manual appears to be silent as to which wing. My opinion is that the offside official (from whom the pass is moving away) has the best look at the forward/backward call, for two reasons: (1) If the receiver is close to the sideline, the near official will have a hard time getting a good angle. He may also be screened by the receiver or a defender. (2) It's just plain more difficult to judge something coming straight at you than moving away.