If the umpire has instructed the team to return to play and they refuse, yes the umpire has the authority to declare a forfeit.
If the team was winning by 4 runs and continued to argue after being told to drop it, pretty dumb move on the coaches part.
This is a grey area.
The Ump never tried to re-initiate play.
The arguing team certainly would have,
but the umpire went from 0 to 100 in a matter of less than 1-minute,
declared the forfeit, and left the playing field.
Both teams still on the field and in their dugouts, in shock at what had just happened.
Did the offensive coach come out screaming at the FU? That's ALWAYS a good way to start with an umpire when question a call. Especially when an umpire has clearly not followed the correct mechanics when making a call.
Going off of your descriptions it sounds like the FU realized he fubar'd when the coach came questioning the call and was looking for a way out. So what happened to the HP umpire? Did he leave with the FU? Did anyone try get the TD or UIC to get the situation straightened out? Did the forfeit stand?
It really bothered me that the HP Ump never tried to take control of the situation and diffuse it.
I later realized that the Field ump WAS the UIC! crazy...
more backstory: apparently, in the pre-game conference at the plate, the field ump expressed his frustration, more than once, that the game was starting about 30min late.
(it was the last game of the day for pool play) I'm sure it didn't help when the head coach said: "I know you are frustrated that the game started late, but please don't take that out on my team, or disrespect my coaches." That's when the game was forfeited.
The forfeit stood.