Michael Ballack is from Goerlitz and, I've just learned, is of Sorbian ancestry. So we may assume that this is a surname of the Slavic speaking minority of South-East Germany, which makes sense considering the -ack ending. It may be the same as the Polish surnames Balak and Ballak, but what any of these names mean I'm unable to say. For some Polish surnames beginning Bal- it's claimed that they derive from the male given name Balthazar. I think I'll leave it at that.