Player control is defined as holding or dribbling the ball. The usual criteria for judging player control is whether the ball came to rest in/on a player's hands(s). And that's always a judgment call.
By rule, there is no player control during a fumble/muff. Soooooo....during a fumble/muff we should be looking for 4 things:
1) a foul because of contact giving one player an illegal advantage
2) player control being established
3) somebody with OOB status touching the ball
4) the offensive team touching the ball first in the backcourt if the fumble/muff went frontcourt to backcourt after having beein in team control in the frontcourt and an offensive player touched it last in the frontcourt.
If a foul occurs, call it. If player control is established, go to the appropriate rule for that situation i.e. traveling, illegal second dribble, etc. If the ball goes OOB or a backcourt violation occurs, call those also.
Other than that, quit thinking so damn much!
KISS!