Complex sentence: During his 19-year major league career of 575 games (including 17 postseason games), he never surrendered a grand slam, nor did he ever allow back-to-back homers.
Split into simpler sentences: During his 19-year major league career of 575 games (including 17 postseason games), he never surrendered a grand slam. He never allowed a grand slam in his major-league career, nor did he ever allow back-to-back homers.