Perhaps not over a balcony, but there was a death at Turner Field in May...
"A Braves fan had been drinking alcohol before he fell down a stairwell to his death at Turner Field during Wednesday night's Braves-Mets game, authorities said....Hayes suffered head injuries when he fell an estimated four levels inside to field level, striking concrete and metal railing, according to Atlanta Police spokesman Ron Campbell.
Campbell said he did not know how much or how long Hayes had been drinking....Hayes was reported to have been sliding on a handrail in the bottom of the 8th inning when he slipped off. He was rushed to Grady Memorial Hospital, where he was pronounced dead."
...in addition to two instances in 2007 (both in New York) of intoxicated people falling down multiple rows of seating and landing on other fans, causing injuries.
AP story from Yankee Stadium
NY Post story from Shea Stadium 
