keep 3 balls in the air while only keeping one ball in the hands at the same time.
keep 4 balls in the air while only keeping one ball in the hands at the same time.
3 balls in total, with 1 ball thrown in between and both have 1 ball. Before you catch the ball thrown, you throw one of your own balls up, catch the bal thrown, throw it back, and catch your own ball etc.
play ball overarm, bounce 1 ball in between via ground.
play 1 ball overarm, play 1 ball over ground.
play 1 ball underhand, roll 1 ball with stretched arms over ground.