In Immaculate Grid Baseball the rule for the "World Series Champ category" is as follows:
Since 1903 (includes Negro Leagues World Series from 1924-27 and 1942-48). When paired with a team, must have appeared in a postseason game (or be on the World Series roster) for the team during the World Series-winning season. When paired with a non-team category, does not need to be in the same season.
Players who appeared for the team in the regular season, but who did not appear in the postseason nor were on the World Series roster, will therefore not qualify for this category. An example of a grid that features this category is Grid #64:
The rule for this category can also be found in the game by either clicking the category header or by clicking the "Rules" link
at the top of the page.