Downwind part of the course. Boat from behind has more wind and is over taking the boat in front. Boat behind tries to pass to leeward of the boat in front. Once to leeward the overtaking now leeward boat calls the windward boat to head up.
The windward boat states, "No, you are an overtaking boat, you have to avoid me"
Leeward boat says, "no, I am now a leeward boat, and I can luff you up"

Both sailors disagree and a little contact is had.

Also you should now, both guys are good friends, this was in winds of 2 knots or less and the boats were sunfish sail boats.

We are just trying to learn the rules better for the next time.

So the question is, when is an overtaking boat no longer an over taking boat and now the leeward boat. Do note, when contact was had, it was the windward side of the leeward boat hitting the leeward side of the windward boat. No contact was had with the stern or bows of the boats(if that matters)

Also, when passing to leeward down wind, how far can you take the windward boat up in a luff tactic?

Granted, these types of situations do not happen that often in cats, but I am realizing I need to get a better grip on the rules.

Last question, what is the best book out there for learning the rules.

Thanks