John Gibson Clarkson (July 1, 1861 – February 4, 1909) was an American Major League Baseball right-handed pitcher.

Born in Cambridge, Massachusetts, Clarkson played for the Worcester Ruby Legs (1882), Chicago White Stockings (1884–1887), Boston Beaneaters (1888–1892), and Cleveland Spiders (1892–1894).

Clarkson compiled a career 328–178 record, placing him twelfth on the MLB list of all-time wins.

Clarkson had a wide variety of curve balls and was considered to be a calculating, scientific pitcher who carefully analyzed every hitter's weaknesses.

Hall of Fame hitter Sam Thompson said of Clarkson: "I faced him in scores of games and I can truthfully say that never in all that time did I get a pitch that came where I expected it or in the way in which I guessed it was coming.

Total Baseball ranked Clarkson as the fourth best pitcher of all time behind Hall of Famers Cy Young, Christy Mathewson and Lefty Grove,[3] though Bill James ranks him lower at number 42 in his The New Bill James Historical Baseball Abstract.

After attending business school and playing semipro ball, Clarkson signed as a free agent with Worcester of the National League in 1882.

The White Stockings finished in fifth place in 1884, but Clarkson put in a strong performance, going 10–3 in 13 starts after being acquired from Saginaw.

Clarkson started three games in the 1885 World Series against the St. Louis Browns, with a record of 1–1 and an ERA of 1.12, allowing only two earned runs in 16 innings.

The 1886 White Stockings finished with a record of 90–34 with a winning percentage of .726 that ranks as one of the highest in baseball history.

After winning the National League pennant by 2+1⁄2 games over the Detroit Wolverines, the White Stockings faced the St. Louis Browns in the World Series for the second consecutive year.

In the bottom of the tenth inning, the Browns' center fielder Curt Welch singled (only the fourth hit off Clarkson) and moved to third on a sacrifice.

Welch and Browns’ third base coach Arlie Latham tried to distract Clarkson with heckling and faking moves toward home.

[4] On April 3, 1888, the White Stockings sold Clarkson to the Boston Beaneaters for $10,000—a huge sum at the time.

Clarkson followed teammate King Kelly, who had been sold from Chicago to Boston the previous year at the same price.

After the 1893 season, Clarkson went on a hunting trip with his close friend Charlie Bennett, who had been his catcher from 1888 to 1890.

After his baseball career ended, Clarkson moved to Bay City, Michigan and ran a cigar store there until 1906.

During a visit with family in 1909, Clarkson fell seriously ill, and was admitted to the McLean Hospital in Belmont, Massachusetts, a well-known psychiatric clinic.