On June 13, 1979, the Astros traded Watson to the Red Sox in exchange for Pete Ladd, cash, and a player to be named later (who turned out to be Bobby Sprowl). Watson played 84 games for the Red Sox through the remainder of the season. He batted .337 with 13 home runs and 53 RBI. On September 15, 1979, Watson again hit for the cycle. Having already hit for the cycle with the Astros in 1977, he became the first player to accomplish this feat in both the National League (NL) and American League (AL).