Port boat is laying the mark, starboard is coming in — who gives way?

Rule 18.3 applies inside the zone at a windward mark: when one boat completes a tack inside the zone and the other boat is fetching the mark on starboard, the boat that tacked must give mark room and must not cause the starboard-tack boat to sail above close-hauled to avoid her. Port tack approaching does not automatically lose — the geometry decides.

<iframe width="560" height="315" src="https://www.youtube.com/embed/Q2xMVr9xLik" title="Sailing Kiwi" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>
<p><a href="https://sailing.kiwi.nz/windward-mark/case-9-tacking-at-the-mark/">Source: Sailing Kiwi</a></p>