Responder's supporting bid at the 2 level, means that he has 6-10HCP and at least 3 cards in the suit. Opener has several possibilities:
With a 1st zone hand (12-14HCP)the side isn't strong enough to go for Game. He can PASS or repeat the major at the 3 level to avoid a possible overcall.
With a 2nd zone hand Opener bids :
- 2 SA; a general trial bid looking for game or even Slam (forcing for a round.)
- 3 in another suit; a trial bid looking for the best game with an unbalanced hand (forcing for a round.)
With a 3rd zone hand 4 in the major suit imposing Game if a Slam isn't possible.