Sunday Starter rule
The Sunday Starter rule, also called the Sunday Pitcher rule is a provision governing the participation of pitchers in the annual All-Star Game. Adopted in 2010, the rule states that a pitcher who starts for his team on the final day before the All-Star break is ineligible to play in the All-Star Game and can be replaced on his league's roster. The rule was softened a bit in the 2012 Collective Bargaining Agreement, giving the affected pitcher the possibility of accepting to pitch in the game, but only for a maximum of one inning or until he reaches a pre-set reasonable pitch count.
The rule was instituted out of teams' concern for the health of their ace pitchers. Because the All-Star Game is normally scheduled for a Tuesday, the final games before the customary break in the schedule take place on a Sunday, i.e. just two days before the game itself is played. Many teams felt that it was not in the interest of a pitcher to be pitching so soon after making a competitive start, and the rule was adopted to ensure that, on the one hand, pitchers were not forced to work in a situation that may be detrimental to their health, and on the other that their being unavailable to pitch would not force their league to play short-handed when home field advantage in the World Series was at stake (something which changed in 2017, when the game became once again a pure exhibition contest).
Pitchers who are replaced because of the rule are still considered to be full All-Stars. They make the trip to the All-Star Game venue, participate in the festivities and are introduced in uniform before the game, but are just not eligible to take part in the game. Since the rule was adopted, there have been one or more pitchers affected each year, with the record being 6 pitchers being replaced for the 2011 All-Star Game.