Still confused by offensive pass interference? You're not alone

The route was a familiar sight to anyone who has watched the New England Patriots on fall Sundays this decade. Tight end Rob Gronkowski lined up in the slot at the 42-yard line. He ran 7 yards to the 35, cut to his right against Carolina Panthers linebacker Luke Kuechly and hauled in quarterback Tom Brady's pass for a 10-yard gain.

This time, however, there was a flag. Referee Jerome Boger had called offensive pass interference (OPI), believing Gronkowski pushed Kuechly during his cut to create separation. The play was a reminder that OPI is one of the most vexing and seemingly random penalties in football, a foul that has been on the uptick this season as evolving offensive schemes stress…