This is a great drill to run for younger, less experienced players. It takes place in a halfcourt setting, and with a minimum of chaos for them to learn the basics of transition basketball.
Have two lines at halfcourt; one on each of the wings. Have one defender positioned around the foul line. Have one ball in one of the lines at halfcourt.
The two offensive players, while maintaining good spacing, run a fastbreak against the defender. A two pass rule is necessary here; it is also necessary to stress to the players that they must get a layup on a two-on-one break. Nothing else is acceptable.
As the players improve, they will begin to understand how to force the defender to commit before making their pass, thereby guaranteeing a layup for their team. It is important to run this drill as fast as possible, because you want to simulate a game-speed situation as closely as possible.