First Black Player In The Majors

May 1, 1884:

Moses Fleetwood Walker became the first black person to play in a professional baseball game in the United States.

In 1884 Toledo joined the American Association, which was a Major League at that time in competition with the National League. Walker made his Major League debut on May 1 against the Louisville Eclipse. In his debut, he went hitless and had four errors. In forty two games, Walker had a batting average of .263. His brother, Welday Walker, later joined him on the team, playing in six games. The Walker brothers are the first known African Americans to play baseball in the Major Leagues.
Walker struggled at first with the bat, but was well regarded for having a rocket for an arm. In 1884, he batted .264, which was well above the league average. A testament to how good Walker was, his back-up was a player named Deacon McGwire, who would go on to a 26 year career, catching 1,600 games.
Walker's teammate and star pitcher, Tony Mullane, stated Walker "was the best catcher I ever worked with, but I disliked a Negro and whenever I had to pitch to him I used to pitch anything I wanted without looking at his signals." Mullane's view hurt the team, as there were a number of passed balls and several injuries suffered by Walker, including a broken rib. There were games where Walker was so hurt, he could only play in the outfield.
Walker suffered a season-ending injury in July, and Toledo folded at the end of the year. Walker returned to the minor leagues in 1885, and played in the Western League for Cleveland, which folded in June. He then played for Waterbury in the Eastern League though 1886.
In 1887 Walker moved to the International League's Newark Little Giants. He caught for star pitcher George Stovey, forming the first known African-American battery. On July 14, the Chicago White Stockings played an exhibition game against the Little Giants. Contrary to some modern-day writers, Anson did not have a second encounter with Walker that day (Walker was apparently injured, having last played on July 11, and did not play again until July 26). But Stovey had been listed as the game's scheduled starting pitcher, in the Newark News of July 14. Only days after the game was it reported (in the Newark Sunday Call) that, "Stovey was expected to pitch in the Chicago game. It was announced on the ground [i.e. "at the ballpark"] that he was sulking, but it has since been given out that Anson objected to a colored man playing. If this be true, and the crowd had known it, Mr. Anson would have received hisses instead of the applause that was given him when he first stepped to the bat." On the morning of that same, International League owners had voted 6-to-4 to exclude African-American players from future contracts. 

In the off-season, the International League modified its ban on black players, and Walker signed with the Syracuse, New York franchise for 1888. In September 1888, Walker did have his second incident with Anson. When Chicago was at Syracuse for an exhibition game, Anson refused to start the game when he saw Walker's name on the scorecard as catcher. "Big Anson at once refused to play the game with Walker behind the bat on account of the Star catcher’s color," the Syracuse Herald said. Syracuse relented and someone else did the catching.

Walker remained in Syracuse until the team released him in July 1889.
Shortly thereafter, the American Association and the National League both unofficially banned African-American players, making the adoption of Jim Crow in baseball complete. Baseball would remain segregated until 1946 when Jackie Robinson "broke the color barrier" in professional baseball playing for the Brooklyn Dodgers' minor league affiliate in Montreal.

Wow, among others, Tony Mullane and Cap Anson were tremendously racist assholes.