To answer the question in the original post, it would fall under Rule 12, Section 3, Article 3: Palpably Unfair Act (Player) -- "A player or substitute shall not interfere with play by any act which is palpably unfair. Penalty: For a palpably unfair act: Offender may be disqualified. The Referee, after consulting his crew, enforces any such distance penalty as they consider equitable and irrespective of any other specified code penalty. The Referee could award a score."
So, the refs probably would have awarded the touchdown and disqualified the player who did it.