I'd already crossed the finish line — how can a starboard boat still protest me?
Because finishing and racing are not the same thing. Under the definition of Racing, a boat is racing until she finishes and clears the finishing line and marks, so crossing the line changed nothing: on port you still had to keep clear under Rule 10. Even once you had cleared, Rule 23.1 would catch you — a boat not racing shall not interfere with one that is. The finish line is not a shield.
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<p><a href="https://sailing.kiwi.nz/v/xXHCscmH_EU/">Source: Sailing Kiwi</a></p>