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Seaver was born in Fresno, California, to Betty Lee (Cline) and Charles Henry Seaver. Pitching for Fresno High School, Seaver compensated for his lack of size and strength by developing great control on the mound. Despite being an All-City basketball player, he hoped to play baseball in college. He joined the United States Marine Corps Reserves on June 28, 1962.

Seaver and the Mets were stunned on January 20, 1984 when he was claimed in a free-agent compensation draft by the Chicago White Sox. The team (especially GM Frank Cashen) had incorrectly assumed that no one would pursue a high-salaried, 39-year-old starting pitcher, and left him off the protected list. Faced with either reporting to the White Sox or retiring, Seaver chose the former. The result for the Mets was an opening in the starting rotation that allowed Dwight Gooden to be part of the team. Seaver pitched two and a half seasons in Chicago and recorded his last shutout on July 19, 1985 against the visiting Indians. In an anomaly, Seaver won two games on May 9, 1984; he pitched the 25th and final inning of a game suspended the day before, picking up the win in relief against the Milwaukee Brewers, before starting and winning the day's regularly scheduled game, also facing the Brewers. After Seaver's 298th win, a reporter had pointed out to White Sox catcher Carlton Fisk that following his upcoming start in Boston, Seaver's next scheduled start would be in New York, and that the possibility existed that he might achieve the mark there. Fisk emphatically stated that Seaver would win in Boston, and then would win his 300th. On August 4, 1985, Seaver recorded his 300th victory at Yankee Stadium against the Yankees, throwing a complete game 4-1 victory. Don Baylor was the tying run at the plate; he hit a fly ball to left field for the final out of the game. Coincidentally, it was Phil Rizzuto Day - Seaver would later become Rizzuto's broadcast partner for Yankee games. Lindsey Nelson, a Mets radio and TV announcer during Seaver's Mets days, called the final out for Yankees TV flagship WPIX.
Tom Seaver