When was the last forfeited game in Major League Baseball and why?

Answer 1

August 10, 1995, Cardinals at Dodgers. It was Free Baseball night at Dodger Stadium. Bottom of the ninth, Cards leading 2-1, Mondesi called out on strikes to open the inning. He complained and was ejected, along with manager Lasorda. Unhappy Dodger fans peppered the field with baseballs. Umpires called in the Cardinals fielders while the grounds crew collected the balls. When play resumed, more balls rained down, and the umpires declared a forfeit in favor of St. Louis.

Box: http://www.retrosheet.org/boxesetc/1995/B08100LAN1995.htm
Known MLB forfeits: http://www.retrosheet.org/forfeits.htm

Answer 2

August 10, 1995:
The St. Louis Cardinals were visiting the Los Angeles Dodgers, and leading the game 2-1 as the Dodgers came to bat in the bottom of the 9th inning. The Dodgers had given away thousands of baseballs to fans coming to the game as a promotion. The first batter, Raul Mondesi, was called out on strikes and then ejected by home plate umpire, Jim Quick, for arguing, as was Dodger manager Tommy Lasorda immediately after. The crowd became agitated, and soon Dodger fans began throwing baseballs onto the field of play. The Cardinals left the field and the baseballs were removed, but when the fans started throwing balls again after the Cardinals came back onto the field, the umpires declared a forfeit by the Dodgers.