Being in an NL-only league it seems like I always have someone going against the Cubs. 99% of the time I pull for the Cubs. That 1% of the time I root for my fantasy player is when the Cubs are down by a bunch, the bases are loaded, and my guy is at bat. In cases like that I root for my fantasy player. If I have a pitcher starting against the Cubs, I hope for a low scoring game that the Cubs win.
From the official rulebook of baseball: "Baseball is a game played between two teams of nine players each." Therefore, baseball is a game played only in the National League.