Lou Bierbauer from Wikipedia
Pittsburgh professional baseball can trace its' roots to 1882, when the Alleghenies joined the American Association. It was called the "Beer and Whiskey" league by the snooty National League because its' owners and sponsors were mostly breweries and distilleries.
The AA wasn't destined to last long, with its' teams and players being siphoned off by the stronger National League. The Alleghenies, one of the AA's original teams, switched to the NL in 1887. But the tale of the Pirates begins in 1890, when some of the AA players revolted.
Growing tension between the ballplayers and team owners led to the formation of the Brotherhood, or Players, League, and several AA players jumped ship. But the Brotherhood League couldn't compete with the other leagues and was out of business after one season.
When it folded, Pittsburgh signed the Brotherhood's Louis Bierbauer, a second baseman. He had been on the roster of the competing American Association's now defunct Philadelphia A's franchise before he switched leagues, and he was supposed to return to his previous club.
But Bierbauer hadn't been placed on the reserved list by the AA through a clerical error and his old team didn't exist any longer, so arbitrators declared him a free agent. (The same was true of OF Harry Stover who inked a deal with the Boston Reds. But since it was an AA team at the time, no hue and cry was ever raised about him.)
Free agency had been one of the sticking points with ownership that caused the players to bolt the AA to form the Brotherhood League. The reserve clause existed even in the 19th century and would last until 1975 when Curt Flood's challenge finally bore fruit. It may be hard to believe now, but Pittsburgh made the first big splash in the free agent market over a century ago.
Signing Bierbauer was considered an "act of piracy" by some, especially in the AA, and the Pittsburgh franchise was branded forever as being "Pirates." The new moniker was embraced by club president J. Palmer O'Neill (he had tried the name "Innocents" the year before and the "Burghers" unofficially before that without gaining much public traction) as he moved his team to the new Exposition Park. The media and fans also took to it, and it became official by the time the first pitch was thrown at Expo Park in 1891.
Bierbauer was the Pirate second baseman until 1897 when he was sold to the St. Louis Browns. He had some solid years with the team, and finished his 13 year career with a .273 batting average.
Steal one player and it stays with you forever.