In Major League Baseball, a few days before each game, each team typically announces a "probable" starting pitcher.
Is there a rule requiring them to do so, or is it simply a matter of tradition or courtesy to opponents and fans? One might think teams could get a competitive advantage by keeping this secret. (Certainly with traditional pitching rotations, it's usually easy to guess who will pitch a given game, but not always, and there are variations.)
There is no rule requiring a team to announce its probable pitcher. Nothing is official until the manager submits his lineup to the umpire before the game begins. But as you said, it is usually very easy to guess who will pitch given the traditional 5-man rotation system.
I remember in the late 80's that the Cardinals (visitors) needed to declare their starters before the Mets (home team). The Cardinals needed to sweep the Mets and the Mets wanted to avoid Dwight Gooden being matched against John Tudor.
