PI mechanics question, 4-man crew

[zm1283]

4-man crew.

For full disclosure, I coach football and have a question because I really don't know how this works.

Does the Umpire in a 4-man crew have pass interference responsibilities on the receivers closest to the sidelines on vertical routes? We had a play where the HL on our sideline was watching the other team's receiver and our corner on a vertical route about 15-20 yards downfield. The receiver had to come back to the ball a little and there was some contact between the two of them, but the HL did not throw his flag. (He did start to reach for it though) The U turned from just behind the LOS and threw the flag for the PI down the field and toward the sideline a considerable distance. We disagreed with the call and I told the HL that if he was going to call the penalty, we may not like it but at least we can buy it since he is right on top of the play, but it looked bad for his U to penalize something from that far away that he could only have seen the very end of.

The U told us that once the ball crosses the LOS he is supposed to turn and watch things downfield, so that is why he threw the flag.

Maybe I am way off here, so if I am, let me know. I just thought it looked like the U stepped on the HL's toes when the play was right in front of the HL. I also realize that if there was a BJ on the field he would have helped the HL, so there are limitations to 4-man mechanics in football.