runner catches ball while in foul territory
 

Here's the situation as told to me...
Batter hits ball down the 3rd base line (one hopper) that first hits in fair territory but then goes over the line into foul territory six to eight feet in front of the base. The baserunner on 3rd who is standing in foul territory instinctively catches the ball.

Should there have been anything other than a foul ball on this play? That is what the crew working the game called.

Any difference in this ruling between NFHS and OBR? A rule reference would be appreciated. Thanks.

If the ball had a chance to go fair, it's INT. If not, it's a foul ball.

Based on your description, the latter applies.

Here's the OBR rule -- it's black and white, but the interp is as I mentioned above w.r.t. having a chance to go fair:

(2) He intentionally deflects the course of a foul ball in any
manner;

Base coaches do it routinely. Foul ball.

If indeed ruled INT the runner would be out. Is that correct?

Yes - but don't even think of calling it on this type of play.

I'm not a baseball umpire, but have seen this play in softball. The call is a foul ball unless the ball had a chance to return fair, which from the OP sounds unlikely.

I had one in softball this year where it was a fair ball because it deflected off the fielders glove. The 3b coach picked it up thinking it was foul. just as the SS was coming over to field it, and she would have had a play at third because that runner also though it was foul and was still at second (and there was a force situation on the play).