On February 1, 1954, St. Claire was traded by Milwaukee with Johnny Antonelli, Billy Klaus, Don Liddle, and $50,000 to the New York Giants for Bobby Thomson and Sam Calderone.
His most productive season came in 1956, when he finished 6–6 with a 3.93 earned run average in a pitching rotation that included Johnny Antonelli (20–13), Rubén Gómez (7–17), Al Worthington (7–14) and Jim Hearn (5–11).
He was later dealt to the Giants along with several other players for Bobby Thomson.
Severo is a first cousin of retired Major League Baseball pitcher, Johnny Antonelli.
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