George Barclay "Win" Mercer (June 20, 1874 – January 12, 1903) was an American pitcher in Major League Baseball from 1894 to 1902.

Born in Chester, West Virginia, he played primarily with the National League Washington Senators (1894–1899), winning 20 games twice with the club.

Appointed player-manager of the Detroit Tigers for the 1903 season, Mercer's baseball career was terminated when he took his own life on January 13, 1903, in San Francisco.

On that day, Mercer shut out Chicago for 11 innings, but the Senators also failed to score a run against opposing pitcher Cy Young.

One Ladies’ Day game in 1897 ended in shambles when women rioted after Umpire Bill Carpenter ejected Mercer.

After Mercer hit .317 in 1897, the Senators began using him as a position player starting in 1898 on days when he wasn’t pitching.

On August 8, 1901, Mercer stole home against the Athletics, becoming the first American League pitcher to accomplish the feat.

However, on January 12, 1903, after a barnstorming tour through the west, Mercer checked into the Occidental Hotel in San Francisco and killed himself by inhaling illuminating gas at age 28.

The watchman of the hotel in making his rounds detected the odor of gas coming from Mercer's room and broke down the door.

Mercer was on the bed with his coat and waistcoat covering his head; and a tube ran from the gas jet into his mouth.

Among the papers found in the room was one which read: 'Tell Mr. Van Horn of the Langham Hotel that Winnie Mercer has taken his life.'

He was twenty-eight years old...."[3] Mercer was laid to rest at Riverview Cemetery in East Liverpool, Ohio.