The hammer play or hammer screen is one of the more common offensive sets used across basketball at all levels because of the simplicity of it. The San Antonio Spurs of the NBA used this play during their early 2000s dynasty as a staple of the offense and were the catalysts of it being so prevalent today. The ball begins the play on a wing either left or right and the ball handler either gets a screen himself/herself or takes it to the rim. On the other side of the court, the center or low post player sets a screen on the opposite wing defender opening up a corner three pointer in a simple and easy play. There are more complex versions and plays that add onto this action but the hammer is quite simple on its own.
After the initial ball handler has passed the ball to the corner, the first option is the perimeter jump shot most likely a three pointer. If this shot is taken away the next offensive option would be the post player in the low post who set the screener for the man who now has the ball. If he isn't open usually a player will flash to the high post and around from the top of the key, creating two more passing options. If none of these look like good options then the ball handler can drive to the rim and the original ball handler could be open in the opposite corner. As you can see, this simple action can create many good chances.
The defense will have to recover from the initial screen and contest the corner three to start off with. After this, the primary defender must stay in front and contest any shooting opportunities from the ball handler while the other defenders must rotate into the passing lanes to limit the good chances the offense can create. Especially around the rim they must deny and keep in front of their offensive players at all times. Once the initial screen occurs, it's difficult to do anything except play the best defense possible and react to the next offensive action.