The Calgary Cannons hit three grand slams in their 22 – 7 win over the Tacoma Tigers. Dave Cochrane, Chuck Jackson and Alonzo Powell connect with the bases full for the Cannons in what is believed to be a first in professional baseball.

On May 16, 1991 — The Calgary Cannons hit three grand slams in their 22 – 7 win over the Tacoma Tigers. Dave Cochrane, Chuck Jackson and Alonzo Powell connect with the bases full for the Cannons in what is believed to be a first in professional baseball.

Source:
Baseball Reference May 16