Have them sit out and rest, then train until they can do the sport without spraining their ankles.
Explanation:
It can seem harsh to have them not participate, especially when they may love the sport, but if they can't get a good handle on how to use their ankles, then you, as the commander, need to take responsibility and have them sit out and regain their ankles so that they don't injure themselves even further. Give them an ice pack, have them train themselves slowly in the sport until they're capable of doing stuff without injuring themselves, then put them back on once they're fine and dandy.
