One of the group tuned on him, slashing him with a machete.
"There wasn't even a fight otherwise we wouldn't of got out of the car," Ms Ludwig told Stuff.co.nz. "All of a sudden he was screaming. The machete went so hard, it went through the bone on each side."
Mr Mutton tried to flee, clamouring over a 2m high fence with his slashed, broken and profusely bleeding arm.
Once over the fence - and safely inside a locked gate - he took his shirt off and used it as a tourniquet while screaming for help.
"I couldn't get to him, he was in there screaming for help. There was blood everywhere, cops and ambulance, and we had to get the fire (service) to use boltcutters to open the gate, I don't know how he managed to jump over the fence."
The scaffolder was set to undergo a lengthy surgery at Waikato Hospital today to repair snapped bones and severed nerves.
Police were investigating the alleged assault and anyone with information was asked to contact Hamilton Police on 07 878 6200 or the anonymous tip line Crimestoppers on 0800 555 111.