Andrew, the Hitter

What do I do? My son Andrew has a serious hitting problem. He doesn't punch or slap, but whenever he gets a hockey stick, bat or some other type of long skinny foreign object in his hands his brother and sister have to run for the hills. (Poor Izzy is yelling for help as I type this; for some reason she gets the brunt of the attacks.) I don't remember either of the other two kids being this way. Any advice on how to approach this?