Question on MLB pitchers

[PMorty]

Ok, i have a question about MLB, whenever there is a game there is this: October 9th MLB LAA(Washburn) against NYY (Chacon) these names are of course a pitcher for each team, however i've noticed these names can change by the end of a game. For example (Washburn) changed to Lackey and now on ESPN's site shows these as (Sheilds) and (Leiter). Can someone inlighten me on the rules of the game and what is this main pitcher that is shown and why it sometimes changes? Sorry to sound so amateur, thanks.

[poolforprofits]

Washburn and Chacon were the projected starters for the October 9th game.
The Angels decided to start Lackey instead of Washburn.
Leiter and Shields are listed as the winning and losing pitchers.
If there's a change in the lead after a pitching change the current pitcher is credited with the win or loss because the starter isn't responsible for the change in the score.

[PMorty]

Thanks for that poolforprofits, makes my system a bit more complicated but anyway, cheers