to decrease the likelyhood of the ankle inverted. If you put on a basketball shoe and try to roll you're ankle (low or high top) you'll see it feels much different and more difficult then if it was a running shoe.

In churchball I've seen 3 fairly severe ankle injuries. 1 was wearing cross country shoes (broken 4th metatarsal), 1 was wearing regular shoes (not sure his injury, but he's still wearing a boot. the other was wearing old, cheap, basketball shoes (but he already had ankle stability issues, and he landed on someones foot which is a recipe for disaster. he cracked his fibula)

shoes make a huge difference.