Leeward Mark Rounding

Maybe only in the Heron fleet?!

Windward boat and port/starboard do apply in the zone, they don't get turned off. A Right of Way boat still has right of way. However the right to mark room overrides them.
In practice that means you have to sail straight to the mark, you can't take a wide sweeping turn.

18.4 Gybing When an inside overlapped right-of-way boat must gybe at a mark to sail her proper course, until she gybes she shall sail no farther from the mark than needed to sail that course. Rule 18.4 does not apply at a gate mark

I'm a bit confused by your description though, I can't quite picture it. Was the leeward boat behind you as you approached the zone and then became overlapped outside you?

Brass, 18.4 doesn't apply because the boats are not overlapped. The OP says that he was clear ahead.

Sounds like a little knowledge of the rules being a 'dangerous thing' in the case of your opponent. I suspect he has recently learned the W/L and P/S still apply in the zone but not that they don't override mark room.......

Originally posted by jeffers If you were clear ahead when the closest boat reached the zone then the boat clear astern shall give Mark Room. Rule 18.2b, c and the definition of Mark Room cover this. 18.2b  If boats are overlapped when the first of them reaches the zone, the outside boat at that moment shall thereafter give the inside boat mark-room. If a boat is clear ahead when she reaches the zone, the boat clear astern at that moment shall thereafter give her mark-room. 18.2c When a boat is required to give mark-room by rule 18.2(b),  (1) she shall continue to do so even if later an overlap is broken or a new overlap begins;  (2) if she becomes overlapped inside the boat entitled to mark-room, she shall also give that boat room to sail her proper course while they remain overlapped. MARK-ROOM, Room for a boat to leave a mark on the required side. Also, (a) room to sail to the mark when her proper course is to sail close to it, and (b) room to round the mark as necessary to sail the course. However, mark-room for a boat does not include room to tack unless she is overlapped inside and to windward of the boat required to give mark-room and she would be fetching the mark after her tack. The W/L rule does still apply but the Leewards boats actions are restricted by the requirement for them to give you Mark Room. 11 ON THE SAME TACK, OVERLAPPED When boats are on the same tack and overlapped, a windward boat shall keep clear of a leeward boat. Need to emphasise the exoneration mechanism here 21 EXONERATION When a boat is sailing within the room or mark-room to which she is entitled, she shall be exonerated if, in an incident with a boat required to give her that room or mark-room, (a) she breaks a rule of Section A, rule 15 or rule 16, or (b) she is compelled to break rule 31. However if there was doubt about the overlap or lack of it then be aware of 18.2e: 18.2e  If there is reasonable doubt that a boat obtained or broke an overlap in time, it shall be presumed that she did not. So, Sapspec8650 When you were five boatlengths from the mark were the boats overlapped?