mechanics question

[Mike L]

Depends on the QB's drop and how quickly the ball is thrown.
While under center, if the QB takes a 3 step drop or less and immediately releases the ball (which is usually the case with this type of drop), the wing is probably in the best position to rule on forward or back. We go with the wing toward the pass rather than the wing away.
More than 3 steps, the wing has now slid down field some depending on what the receivers are doing and his focus isn't toward the QB and the R now has a better angle to make the call.
In the shotgun, it's the R.
In a scramble, it's again going to be the R.