Pinned and can't tack
The situation
Mid-fleet upwind, Theo is pinned: a boat sits right on his windward hip, so he can't tack without hitting her, and he's stuck in bad air.
The question
Can he just tack and make the windward boat get out of the way?
The ruling
No. If he tacks, rule 13 gives him no rights until he's close-hauled, so tacking into the windward boat is a foul. And rule 20 (room to tack) doesn't help — that rule only applies when he needs to tack to avoid an obstruction like a shore, not because a boat is sitting on him. His real options are to wait for the windward boat to tack or peel away, foot off to find clear air, or build a gap and then tack cleanly. Being pinned is a tactical problem, not one the rules will solve for him.
A boat on your hip isn't an obstruction — you can't demand room to tack. Make your own gap, then tack (rules 13, 20).
Opens the situation on the boat-length grid — scrub it and see exactly how the boats meet. Free, no account needed.
Rules cited
See the underlying rule: Rule 13 — While Tacking.