It is always fun to attack something that seems to be under-defended, however, you should always assume that your opponent is going to see the threat and respond to it. If your opponent is forced to put his pieces on awkward squares where they inhibit his development, that may be good reason to violate the general opening principle of "move every piece once before you move any piece twice." In fact, White frequently has the opportunity to make those kind of moves in the Evans Gambit. In this case however, Black meets the threat with a move that he was eager to make anyway, 9...0-0. White would have been better completing his mobilization with 9.d4.
Just a Pawn
One of the things that makes chess so frustrating is how a minor oversight can have such dire consequences. On 3rd Board, Meadows' Ben Kusnierz had played very solidly against Echo Genc for twenty-three moves before he missed a knight fork that netted Echo a pawn. Unfortunately for Ben, the loss of that one pawn left him with two isolated pawns which soon became targets.