If you want to represent this in your games, here is a simple rule for you:
Any "goblin" creature (goblins, orcs, hobgoblins, others as determined by the GM) that is reduced to exactly 0 hit points (in other words, the killing blow is exactly equal to the creatures remaining hit points) will set the creature into goblin frenzy.
While frenzied, the creature will attack with a +2 bonus to attack rolls, and +1 bonus to damage. It will ignore any morale effects and will shrug off any mental spell effects directed at it (including charms, sleep and similar).
The monster will make a free attack immediately at a target in melee range, and will then attack on it's normal turns. If using individually rolled initiative, the berserker attacks at a
Any additional damage will kill the frenzied creature for good.