Situation 1
Red completes her tack slightly to leeward and on the limit of being overlapped with Green. Green’s only option is to sail above close hauled to avoid contact with Red.

Question
Did Red break rule 18.3?

Answer
Yes.

Red caused Green to sail above close-hauled to avoid contact. All other requirements of rule 18.3 were met.

Situation 2
Red completes her tack a quarter of a boat length ahead of Green. Green could have sailed either to windward or to leeward of Red. If Green had sailed to leeward of Red, she would not be able to pass the mark on the required side. Green sailed to windward of Red and sailed above close-hauled to avoid contact with Red

Question
Did Red break rule 18.3?

Answer
Yes.

See answer 1.

Situation 3
Red completes her tack a quarter of a boat length ahead of Green. Green could have sailed either to windward or to leeward of Red. Green sailed to leeward of Red. Red does not give Green mark-room. Green passes the mark on the wrong side.

Question
Did Red break rule 18.3?

Answer
Yes.

After passing head to wind from port to starboard tack inside the zone, Red did not give mark-room to Green who was overlapped inside her.

Situation 4
Red completes her tack a quarter of a boat length ahead of Green. Green could have sailed either to windward or to leeward of Red. If Green had sailed to leeward of Red, she would clearly be able to pass the mark on the required side. Green sailed to windward of Red and sailed above close-hauled to avoid contact with Red.

Question
Did Red break rule 18.3?

Answer
Yes.

Green may choose between the two options available to her, and there is no rule that binds Green into one of the two options.

Situation 5
Red completes her tack a quarter of a boat length ahead of Green. Green could have sailed either to windward or to leeward of Red. Green sailed to leeward of Red. Red gives Green mark-room.

Question
Did Red break rule 18.3?

Answer
No.
Red complied with the requirements of rule 18.3.

NOTE
Rule 18.3 does not only apply when luffing above close hauled is the only viable solution.

The word ‘cause’ in the rule refers to a cause-effect relation between the actions of the port-tacker and the boat sailing on starboard. In the situations above, when the action of Green is a result of Red’s actions, the ‘cause’ clause of rule 18.3 is satisfied, even if there was another way to avoid the boat that tacked.