Dave Matthews has a long standing feud going on with Brian Calhoun.
Calhoun works for the brand of guitar that Dave has been using for a long time, Rockbridge, and the two have become friends since Dave works so closely with the company on his guitars.
Like any good friends, they have their pranks and theirs is the slap fight. While some of the slaps may look staged, there are a few that are complete surprises. I laughed at each one anyway and had to watch it a few times.