The best way to approach it is to use common sense. If you lack in that department, then Sorry, can't help much. The intent of the rule is to protect the student athlete. Just as in NCAA, remember that phrase, you can't go wrong. If your a rule book ump, your heading for a lot of arguments in your career. If you can apply the rule with the "spirit and intent" in mind, than you most likely don't. R1 didn't alter anything, simply sliding with his lead foot to the outside of the bag shouldn't trigger anything. Where is his body? If it's over the bag, nothing. Sliding with his body outside the bag should and will, NCAA as well as FED. Protect the fielder. Also, remember in FED, R1 can't slide through the bag and make contact with F6 behind the bag. If F6 is in front of the bag, again, you have nothing. In NCAA R1 can now slide through the bag. Seems some coaches were teaching their kids to stay behind the bag for the interference...NO
Needless to say, when they moved up, they couldn't turn a pivot. Duh. Hope that helps