unsportsmanlike act affected the play. If they do, they have the authority to penalize however they deem appropriate, up to and including either negating or even awarding a TD.
If a person on the sideline trips up a player who was obviously headed for the end zone, the refs can award the TD.
In the game on Saturday, I don't think we know whether or not the refs would have negated the TD as they never had to make that decision. However, odds are they would not have negated the TD as I haven't seen any evidence that Harlan's actions affected the play.