John Wesley Glasscock (July 22, 1857 – February 24, 1947) was an American shortstop in Major League Baseball who played for several teams from 1879 to 1895.

When he retired he ranked fifth in major league history in games (1,736) and at bats (7,030), seventh in total bases (2,630) and eighth in doubles (313).

In mid-1884 he jumped to the Cincinnati Outlaw Reds of the Union Association during that league's only season of play and batted .419 in 38 games.

He also set new major league records for assists (493) and double plays (58), topping Fennelly's totals of 485 and 54 with the previous year's Red Stockings.

Early in the year, he discovered 17-year-old future Hall of Famer Amos Rusie pitching for a local semi-pro team, and the young hurler was promptly acquired for Indianapolis.

Glasscock had been intending to switch leagues as well but was expelled from the Brotherhood of Professional Base Ball Players after signing his 1890 contract with Indianapolis.

He won the 1890 batting championship by eleven points over Billy Hamilton, going 6-for-6 on September 27; he also became the second player to lead the NL in hits two years in a row (joining Brouthers), and was second in doubles to Sam Thompson and fifth in total bases.

He batted .280 in his last full season in 1894, leading the NL in fielding for the last time with a .933 average, and ended his major league career in 1895, splitting the year between the Louisville Colonels and the Washington Senators.

He played a notable role in the advancement of defensive tactics, being one of the first shortstops to use signals indicating which infielder would cover second base on steal attempts, and also one of the first to back up throws to the second baseman.

Germany Smith broke his records for career assists and total chances in 1897, and his mark for games at shortstop in 1898.