No punches were thrown or anything like that, which is the norm these days. As you can see in the video, it all stemmed from Lee throwing inside to Span after he tried to call time during the lefty's wind-up. Pitchers don't like that kind of stuff.
Since the whole thing blew over without incident, the only reason this brawl is noteworthy is this excellent GIF of Span saying "come on, man" after the pitch by Lee:
(GIF via NotGraphs)