It's multiple of them. Not just one.
They are supposed to be big goons(the REAL ones) that mainly use their bare fists due to surviving multiple bullets. There weak spots are their head and legs. Mainly, you shoot a bruiser in the legs to stagger them, than you go for their head as they are between 7-8 feet tall. But they sometimes are equipped with Light Machine Guns or Heavy caliber pistols(50.AE Desert Eagle for example)