Mark Henry Belanger (June 8, 1944 – October 6, 1998), nicknamed "The Blade", was an American professional baseball shortstop. He played eighteen seasons in Major League Baseball (MLB) for the Baltimore Orioles and Los Angeles Dodgers. A defensive standout, he won eight Gold Glove Awards between 1969 and 1978, leading the American League in assists and fielding percentage three times each, and retired with the highest career fielding average by an AL shortstop (.977). He set franchise records for career games, assists and double plays as a shortstop, all of which were later broken by Cal Ripken Jr. After his playing career, he became an official with the Major League Baseball Players Association.
Belanger was born in Pittsfield, Massachusetts, where he attended Pittsfield High School, where he played baseball and basketball. On the basketball court, he became the school's first 1,000-point scorer. He was recruited by the Orioles as an amateur in 1962, and made his debut with the club on August 7, 1965.
He took over as the Orioles' regular shortstop in late 1967, and held the position for over a decade. Nicknamed "The Blade" because of his height of 6 ft 1 in (1.85 m) and weight of only 170 lb (77 kg), Belanger was known as a poor hitter. In 1970 he was a Triple Crown loser (finishing last in the TC categories). In his eighteen seasons in the major leagues, Belanger hit only 20 home runs, and had a lifetime batting average of .228, only topping the .230 mark over a full season three times; his .228 average is the third-lowest of any major league player with over 5000 career at bats, ahead of only George McBride (.218) and Ed Brinkman (.224), and the seventh-lowest of any non-catcher with at least 2500 at bats since 1920. His true contribution to the team was on defense, where he earned a reputation as one of the best fielding shortstops ever. Receiving the AL Gold Glove eight times (1969, 1971, 1973–78), he was also named to the All-Star team in 1976. Belanger joined a select group of shortstop-second baseman combinations who each won Gold Gloves in the same season while playing together: in 1969 and 1971 with Davey Johnson, and again with Bobby Grich each year between 1973 and 1976 inclusive. And with Brooks Robinson winning at third base every year through 1975, the left side of the Orioles' infield was seemingly impenetrable.
He hit a rare home run in the first American League Championship Series game ever played in 1969, and after uncharacteristically hitting .333 in the 1970 ALCS, his contributions led to the Orioles' 1970 World Series victory, the team's second title in five years; he caught a line drive to end a 4–3 victory in Game 1 with the tying run on first base, and had an assist to end Game 3. Playing in six ALCS, he set league playoff records for career games, putouts, assists, total chances and double plays by a shortstop, all of which were broken between 1998 and 2002 by Omar Vizquel and Derek Jeter.
Following Belanger's departure from the Orioles, former teammate Rich Dauer said, "Anyone would miss Mark Belanger. You're talking about the greatest shortstop in the world. He never put you in a bad position with his double-play throws...He'd put you where you should be to make the play... I never had to think out there. If there was any question in my mind, I'd look at Blade, and he'd have a finger out, pointing which way I should move.
Belanger served as the Orioles' union representative for several years. He was one of the four players who led negotiations during the 1981 strike. After his retirement as an active player he was employed by the MLB Players Association as a liaison to its membership.