Robert Brown Thomson (October 25, 1923 – August 16, 2010) was an American professional baseball player, nicknamed "the Staten Island Scot". He was an outfielder and right-handed batter for the New York Giants (1946–53, 1957), Milwaukee Braves (1954–57), Chicago Cubs (1958–59), Boston Red Sox (1960), and Baltimore Orioles (1960). His pennant-winning three-run home run for the Giants in 1951 is popularly known as the "Shot Heard 'Round the World", and is one of the most famous moments in baseball history. It overshadowed his other accomplishments, including eight 20-home-run seasons and three All-Star selections. "It was the best thing that ever happened to me", he said. "It may have been the best thing that ever happened to anybody."

Thomson was born in the Townhead area of Glasgow, Scotland, United Kingdom. He was the youngest of six children born to parents James and Elizabeth. He arrived in the United States two years later. James, a cabinet maker, had moved to New York City shortly before Bobby's birth and sent for his family in 1925.

Thomson grew up on Staten Island in New York City and signed with the New York Giants for a $100 bonus right out of Curtis High School in 1942. On December 5, 1942, he joined the United States Army Air Forces and trained as a bombardier. His entire service was within the continental United States. He played semiprofessional baseball in the summer of 1945 while awaiting his discharge.

Thomson batted .283 with 29 home runs and 82 runs batted in (RBIs) in his rookie year, 1947. The following season, he batted .248 with 16 home runs. In 1949, Thomson had career bests in RBIs (109) and batting average (.309). His batting average dropped to .252 in 1950. He then hit a career-high 32 home runs in 1951, the fifth-best total in the major leagues; he also had the fourth-highest slugging average in baseball that year.

Thomson became a celebrity for his walk-off home run off Brooklyn Dodgers pitcher Ralph Branca to win the 1951 National League pennant. The home run, nicknamed the "Shot Heard 'Round the World", was dramatic as, until 1969, league pennants were only decided by a playoff when the teams involved finished the regular season in a tie. Prior to 1951, playoffs had only been necessary in 1946 (NL) and 1948 (AL).

Although in mid-August, the Giants were 13+1⁄2 games behind the league-leading Dodgers, they won 37 of their final 44 games to tie Brooklyn on the final day of the regular season, forcing a three-game playoff. The Giants won the first game 3–1 as a result of a two-run home run by Thomson (off Branca). Brooklyn's Clem Labine shut out the Giants in the second game, 10–0. The decisive contest, played on October 3 at the Polo Grounds, was the first major sporting event televised coast-to-coast in the United States. The Dodgers took a 4–1 lead into the bottom of the ninth inning, but Giants shortstop Alvin Dark singled, advanced to third on a single by Don Mueller, and scored on a double by Whitey Lockman. With Lockman on second and pinch runner Clint Hartung at third, Thomson's walk-off home run turned looming defeat into a 5–4 victory. The moment was immortalized by Giants play-by-play announcer Russ Hodges's excited multiple repetitions: "The Giants win the pennant! The Giants win the pennant!"

Waiting in the on-deck circle to hit behind Thomson was rookie Willie Mays. The Giants' season ended, however, at the 1951 World Series; the Yankees swept the last three games to win the best-of-seven series, four games to two. Thomson went 6 for 21, batting .238 in the series with no home runs.

The bat from the "Shot Heard 'Round the World" is in the collection of the National Baseball Hall of Fame and Museum in Cooperstown, New York, as are the glove and the spikes Thomson used at the game, though the home-run ball he hit has never been definitively identified. The uniform worn by Thomson on that day is apparently a part of a large private collection owned by Dan Scheinman, a member of the San Francisco Giants ownership group.