I had a single hammerdwarf hold off a whole goblin siege. My fortress, clapbronze, was a hollowed out mountain, surrounded by a magma moat spanned by a single, narrow bridge.
One dwarf was outside the moat, fishing, when the siege hit. I activated my military and commanded them to muster at the fortifications around the bridge's guardhouse, a convienient trapped bottleneck on the safe side of the moat. My lone fisherman activates and becomes a hammerdwarf.
He reaches the bridge as the goblins do, the rest of my military is nowhere to be seen. I tell him to hold his position.
The goblins pepper him with 10 combat pages of arrows, mostly to the head, before their infantry hits him. Carnage esnues. He slams greenskin after greenskin off the bridge, into the lava two z levels below and four z's deep. Throught the combat, almost every one of his bones are shattered, as well as his spine and skull, but he fights on. The goblin infantry dispatched, he charges the archers. They flee. He cripples two, and kills a final one by biting him. In the mouth. From behind.
His job done, he calmly strolls to the hospital. In spite of his wounds, his gushing blood loss and his splintered nervous system he is not sick once. He is in surgery for two seasons. During this time a vast and elaborate crystal tomb is prepared for him, containing crafts carved from the goblins he slew and barrels of their blood. He lives. His tomb becomes his new bedroom. He is declared a militia captain and given an artifact mitten as his reward.
His skill as a hammerdwarf has been proven. His is no longer "dabbling". He is adequate.