If he gets past head to wind and onto the starboard tack, you now have to avoid him...technically. However, the game will usually penalize the port tacker in that case (just like in real life, you roll the dice by getting into a situation that will involve penalties and/or judges). In a nutshell - the longterm starboard tacker must avoid the guy that just tacked in front of him that is now on starboard - even if it means slowing down (no rule gives right of way to a boat that would hit another boat from astern). This is a dirty translation...but if the longterm starboard tacker can't possibly avoid the port tacker (whether or not the port tacker made it to starboard before hand), the port tacker "tacked too close" and is at fault. If the long-term-starboard tacker could have avoided them by either slowing down or steering up past close-hauled but still hit them, the starboard tacker is at fault (on two rules).

Things get a little tricker within the two boat length circle...If you are in the two length boat circle of the mark, the port tacker can come in and tack in front of a starboard tacker - but MUST be on starboard tack before the other boat has to avoid and MUST not make the starboard tacker go past close hauled to avoid.