The Toronto Maple Leafs play their home opener against the Jersey City Jerseys. Toronto outfielder Ellis Burton hits a two-run homer batting from the left side in the 8th inning – then hits a grand slam from the right side later in the frame. It is the first time in Organized Baseball history that a player has homered from both sides of the plate in one inning.

On May 3, 1961 — The Toronto Maple Leafs play their home opener against the Jersey City Jerseys. Toronto outfielder Ellis Burton hits a two-run homer batting from the left side in the 8th inning – then hits a grand slam from the right side later in the frame. It is the first time in Organized Baseball history that a player has homered from both sides of the plate in one inning.

Source:
Baseball Reference May 3