[officialtony]

This would be a ground rule I will cover before the game if I am aware of the circumstance. I would rule this a foul ball or dead ball ( whatever the concensus is between coaches )if it hits the overhead fence over fair or foul territory. No other way, in my mind, to play this for fielders and batters.
If it happens to me the first time I am at this field , I would have to halt play and call it it a foul ball or maybe dead ball. Really need to think it over. But no way would it be a live ball. My humble opinion.