I don't know how much the fine is, but there IS a fine. Actually, the folks in Wrigleyville (arear around Wrigley Field) want the law vigorously enforced. Seems one of their problems with night games is fans urinating on their lawns and such.
Be sure to go to Sluggers and The Cubby Bear. Also get down to Division Street for some fun bars. We have neighborhood bars all over the place and they all have their own "charms".