It depends on how your league is set up with scoring options. Under 'Offense - Miscellaneous' there are two settings to select from. These are "Fumble" and "Fumble Lost." Most leagues have fumble lost as the selected item, but here is the difference in settings.
Fumble would be the instance a player loses the ball from his possession, regarless of who recovers the ball.
Fumble Lost is when a fumble results in a change of possession.