Just whatever you do, don't use a piddly weapon to piss him off. Commandos are bad about this. Yes, the bullpup is great, but no, not even a full clip into the Fleshpound's face will kill it. That just makes it mad. Same for snipers who think they can WTFPWN it with one headshot...no...just angering it...
Another important thing is that after a berserk charge, they stop berserking. IF someone is getting mauled, they can run until it unberserks (Almost definitely taking a hit, but just one hit, not a series of them!) and then back away, making a PLAN to tackle it. If everyone unloads on it like mad when it charges someone, it'll unberserk after hitting him, then IMMEDIATELY berserk again and continue whaling on the poor guy, usually ending him...THIS, imo, is what gets about 2/3 of the Fleshpound victims killed...