I'm wondering that if someone uses a move with higher priority than the move Sucker Punch, will Sucker Punch work?
Because technically, the opponent did attack...just not after Sucker Punch was used. What would happen?
Sucker Punch would fail in this case.
If the target uses a non-damaging move or happens to act before the user, Sucker Punch will fail.
http://bulbapedia.bulbagarden.net/wiki/Sucker_Punch