In a 9 – 7 loss to Oakland at Royals Stadium, Danny Tartabull of the Royals becomes the first Royal to hit three home runs in a game.

On July 6, 1991, In a 9 – 7 loss to Oakland at Royals Stadium, Danny Tartabull of the Royals becomes the first Royal to hit three home runs in a game.

Source:

Baseball Reference July 6