William Lester Demars
- Bats Right, Throws Right
- Height 5' 10", Weight 160 lb.
- High School New Utrecht High School
- Debut May 18, 1948
- Final Game September 28, 1951
- Born August 26, 1925 in Brooklyn, NY USA
Billy DeMars began his playing career in 1943 and was active until 1958, with 9 appearances in 1959 and 1960 as a player-manager. He missed the 1944 and 1945 seasons due to military service in the US Navy. He was the radio man on a Consolidated PBY "Catalina" search and rescue amphibious aircraft.
He played parts of three seasons in the major leagues, first hitting .172 in 18 games for the Philadelphia Athletics in 1948. In 1950, he got his most extensive look with the St. Louis Browns when he hit .247 in 61 games while sharing the shortstop with Tom Upton. In 1951, he came back for one game with the Browns at the end of the season, going 1 for 4. Overall, he hit .237 in 80 games, with only 6 extra-base hits and no homers, but did draw his share of walks, giving him a respectable .326 OBP.
DeMars managed in the Baltimore Orioles system from 1958 to 1968. On June 14, 1966, his Miami Marlins defeated the St. Petersburg Cardinals, 4-3, in a game that required 29 innings and was the longest game played in organized baseball history until then. DeMars left managing and the Orioles in 1969, becoming a coach for the Philadelphia Phillies, where he stayed through 1981. He coached for the Montreal Expos from 1982 to 1984, and finally for the Cincinnati Reds from 1985 to 1987. Pete Rose was the link between the three stops, playing with Philadelphia from 1979 until his departure, joining the Expos in 1984 when he was a coach, and then inviting him to serve under him as a coach when he was the Reds' player-manager in 1985. During those years, he had a reputation as a top-rank hitting coach, even though he hadn't been much of a hitter himself.
When he joined the Expos' coaching staff, he joked with reporters that the city of Montreal had gone out of its way to welcome him, naming a metro station after him. He was referring to the "Champ de Mars" metro station, in old Montreal, which is actually named after the city's 18th century military exercise grounds.