Water at the mark
The rights of way at a mark of the course depend on what type of buoy is being rounded.
There is no right to water at a start buoy (or committee boat). Starboard has rights over port. Leeward boats have right of way over windward boats and can luff them as high as head-to-wind before the start gun. Boats can be pushed the wrong side of the start buoy by a boat below them.
Calling water at the mark
If an overlap exists at three boat lengths from the mark, the inside boat can ask for room to round the mark from outside boats. If an overlap is created or lost after the three boat zone this does not effect the right of way. If there is no overlap at three boat lengths from the mark, boats behind must allow boats ahead to round the mark ahead of them.
You can call water on boats on the same tack at a windward mark but starboard boats have right of way over boats on port tack. You cannot cause a boat that is fetching the mark on starboard to deviate from their course within the three boat length zone even if you have completed your tack onto starboard in front of them.
At the end of a downwind leg within the three boat length zone, starboard boats do not necessarily have right of way over port tack boats. Right to water over-rules starboard and port.
An overlap extends out to infinity perpendicular to a boat. Overlaps may occur a long way from a boat entering the zone. Inside boats are entitled to call water on outside boats but no foul occurs if the outside boat can round the mark before the boat calling water can reach that boat.