I do believe Affleck wears a hairpiece, but I don't believe the story about it coming off in horseplay.

I re-attach once a week, and there is no way my piece would come off in horseplay. Obviously, if someone pulled really hard they could pull some of the hair out of it, just like they could pull my real hair out. If they got me when I have been sweating heavily they could probably pull my front hairline up (which would be embarrassing enough), but there is no way they could pull the whole unit off without taking chunks of my scalp with it. Affleck is hardly going to stick his system on with a bit of chewing gum and hope for the best - he has too much to lose.

I suspect what happened is that the newspaper which wrote this story was told by an insider in Affleck's circle that he wears a piece, and rather than just saying "we hear he wears a piece" they wrote this voyeuristic story in the knowledge that Affleck would never be able to sue them.