The first exercise in this video is shielding the soccer ball. It is important to instruct the player to get low, keep a wide base of support, and to keep the core engaged in order to maintain balance. Also, the player on the ball should not excessively lean into the defending player because that will cause them to lose balance when the defender moves. The player on the ball should be able to react quickly to a direction change with a single step or hip switch. Cue the players to avoid excessive knee valgus (external cues work best).
The second exercise is seated juggling. In this variation, the player should keep both feet off the ground at all times in order to engage the abdominals. Youth and novice players can try one juggle at a time, and progress to multiple juggles in a row. Encourage athletes to keep their chests high in order to avoid excessive rounding of the back.
In the third exercise I perform a side plank (my favorite core exercise) with a side volley. Player should keep their hips up off the ground and maintain a straight line from the back of their heads to their heels.
In the last progression, I have the athlete juggle the soccer ball while a teammate gives them gentle external perturbations. This forces the player to not only react to where the ball goes, but also to keep his core engaged in order to maintain balance during the perturbations.