Looks like the folks at Foxconn got a little rowdy. Macrumors is reporting that the riot involved about 2,000 workers and that according the official company line it started as a personal dispute between workers. The workers are saying otherwise.
While Foxconn is notorious for the poor working conditions for workers who make Apple products, remember that most major computer manufacturers deal with Foxconn in some capacity. Macrumors also reports that workers are saying that it was started when guards started beating workers. Check out Macrumors for the whole story.