checking

Blinds are 10 and 20. Player to the left of big blind bets 50. All players stay in to see the flop. So, all have bet 50 at this point. Betting goes to small blind. Question: Can 'small blind' player check to stay in the game, or does he have to bet the minimum of the raise before the flop (which was 50 - 20 = 30)?

The SB player can check at this point since this is a new betting round.