The official GemStone IV encyclopedia.
Shield Spike Mastery is a passive shield specialization that gives you a chance to reactively spike foes after blocking their attacks with a spiked shield while in a forward or greater stance. At rank 1, this applies only to brawling or natural weapon attacks; at rank 2 it applies to all melee attacks.
A Grimswarm troll guard thrusts with a trident at you!
With extreme effort, you block the attack with your greatshield!
You manage to angle your mithglin greatshield just right so that the troll guard comes perilously close to the spikes on it!
A spike on your mithglin greatshield jabs into the troll guard!
... 10 points of damage!
Strike to right hand breaks a fingernail!
A Grimswarm troll soldier's flesh wounds regenerate quickly.
A Grimswarm troll soldier's abdomen regenerates and looks much better.