Clawhammer banjo is a style of playing
the 5-string banjo originating in the
Appalachian mountains, and predating
the more common bluegrass styles (known as Scruggs style, finger-style
and also related to melodic 5-string banjo). It involves only the back of one fingernail and the thumb, and it looks more less like you're punching the head of the banjo. It's
most common in old-time music accompanying a fiddler. See Mark Schatz, Bob Carlin or Stephen Wade for excellent picking.