The National Football League Players Association (NFLPA) went on strike in 1987, and the owners brought in replacement players to start the season. After three weeks, many of the players on strike returned, weakening the union's position.
In 1994, the Major League Baseball Players Association (MLBPA) went on strike. Spring training in 1995 started with replacement players, however the dispute was settled before the start of the regular season. Players who agreed to serve as replacement players were subsequently blacklisted by the MLBPA, although the majority of them had not been eligible to join the union at the time they crossed picket lines, since they had not played in the major leagues.
In 2005, the labor conflict between the United States Soccer Federation and its players led to U.S. national team players not reporting to camp in lieu of qualification for the 2006 World Cup. With almost every single Major League Soccer player, even those not in the U.S. player pool, refusing to participate, the camp was made up from players from the lower divisions of US Soccer, the United Soccer Leagues. The two sides came to an agreement before any matches were played.
Though not technically players, professional officials have associations very similar to players associations.
The National Hockey League Officials Association struck in 1993. The league decided to bring in replacement officials, however many officials from the minor leagues and high-level junior hockey stood with the union and refused to break the picket line. This led to the resolution of the strike after 17 days.
In 1999, 22 Major League Baseball umpires resigned since their collective bargaining agreement did not allow them to strike. The 12 umpires who decided not to resign were joined by 25 replacements. The umpire's posturing was unsuccessful and led to a lengthy legal battle. In the end, some - but not all - of the umpires who resigned were rehired, and a new union, the World Umpires Association, was created to represent the umpires.