9 Year Old Hitting Help

A tennis ball gives little feedback to the hitter. Hit it at the end, middle, or handle of the bat and there's no vibration. When your son hits baseballs, he experiences much more vibration from the off-center hits, so he becomes afraid to swing hard. By reverting back to the tennis balls, he isn't learning about the "sweet spot" of the bat. Stick with real balls or batting cage balls. He'll soon learn how to adjust his body to contact the ball with the meat of the bat or to lay off the bad pitches entirely.