September 14, 1990 -
Ken Griffey, Sr and and his son
Ken Griffey, Jr., playing together for the Seattle Mariners, hit back-to-back home runs in the 1st inning of play.
In 1990 and 1991, Griffey and his father became the first son and father to play on the same major league baseball team at the same time. The duo are the only father and son pair to hit back-to-back home runs.