From the Enquirer:
The slam was the big blow for the Reds in an 8-7 loss to the Chicago Cubs.
It came off former Red Ryan Dempster. Dempster once dressed down Lopez on the field for not throwing home on a play. Dempster later apologized, but Lopez had not forgotten.
"It happened," Lopez said. "But I wasn't thinking about it. But now that you mention, yeah, it was great to hit it off him."
I had forgotten about that Dempster incident, but I remember it really ticking me off at the time that a pitcher as mediocre as Dempster had the gall to call anyone out. Dempster and Chicago seem like a pretty good match for each other.