3 rows about 1.5 meters from the net. Serve 3 at a time and then get the ball yourself and join the back of the row again.
Increase distance
Team formation. Also here we take a field of level 3. Per trainer 1 team. Trainer throws the ball over the net and the team catches the ball and throws the ball over the net again. Then turn around immediately and keep looking at the opponent/trainer. The line-up is a bowl