I once saw Steven Mackey and Jennifer Koh perform Mackey's double concerto Four Iconoclastic Episodes with the LA Phil (John Adams conducting). They were in the middle of a particularly aggressive section when the bridge on Jennifer Koh's violin snapped in half. They stopped the show and she traded violins with one of the violinists in the back row and jumped right back in. It was one of the most bad-ass things I've seen happen in a concert hall.
Mario Godoy