When a batter becomes a runner by putting the ball into play with the bat, the official scorer must decide if in doing so, the batter/runner made it to base because of good placement, or because a fielder chose to make an out at another base or made an error. If the batter makes it to base based on the the merit of putting the ball into play with their bat, the scorer can award a base hit to the batter/runner. If the batter runner makes it on base due because a fielder chose to make the out at another base, the scorer notes FC (fielder's choice) on the score sheet.

Hope that helps

It is when the fielder decides on what play to use to get a runner out when given 2 or more possible situation after a hit happens

http://www.softballperformance.com/softball-fielding/developing-a-middle-infielder.html

thanx