Irish was the older brother of Bob Meusel, also a star outfielder. The two faced each other in three successive World Series (1921-23), Irish playing for the Giants, Bob for the Yankees. Though of Alsatian heritage, Irish got his nickname because he looked Celtic. He had seemed lackadaisical as a .300-hitting Phillies outfielder. John McGraw obtained him in July 1921 and made him the cleanup batter for the Giants team that won four straight pennants, 1921-24. Irish hustled in the field for the acerbic McGraw. He had over 100 RBI each year from 1922 to 1925, with a career-high 132 in 1922, and a league-high 125 in 1923.