About the only other player that 'might' be in foul territory would be F3 holding a runner, or in youth league, F5 holding a runner on 3rd. In the real world, I have never had anyone ever say anything about an F3/F5 having a foot in foul ground prior to the pitch.
As mentioned, if someone complains, then both teams have to comply. I would simply say to the offending player, 'get in fair ground'. But, I've never had an occassion to enforce it.