Francisco Cervelli was at the plate for the Pirates in a game the Cubs were leading 6-4. On a pop-up behind the plate, Anthony Rizzo went to field it and a fan appeared to interfere, costing the Cubs the out. Later in the at-bat, Cervelli doubled, just barely missing a home run. Two batters later, Starling Marte knocked in Kevin Kramer (who ran for Cervelli) and Kevin Newman to tie the game at 6-6.
At press time, the Cubs are coming to the plate in the bottom of the ninth and could undo this damage if they score a run for the walk-off.
UPDATE: The Cubs won on an Albert Almora walk-off in the 10th inning, so this is all merely a footnote.