A fumble is when a player with the ball drops it.
loose ball (fumble)
"FF" stands for "Forced Fumble" When a player knocks the football loose or strips the ball from a player that has full possession of the football is considered a Forced Fumble (FF).
Yes. There was a rule in college football where the defense could not advance the ball after recovering a fumble but it was abolished in 1992.
To signify a fumble.
If the 'kick' is intentional, it is an illegal kick penalty. If it is unintentional, it is a fumble.