If the standard is that there can only be a rivalry if fans of both teams consider the other team to be their biggest rival, then the Brewers don’t have a rival. But, I don’t buy that definition. I think the Cubs are by far the Brewers biggest rival these days, mainly because of the numbers of Cubs fans who come here when the Cubs play and how too many of them behave when they’re here. Plus, starting in 2007, the Brewers and Cubs have been involved in several division races together. The Cardinals are in a similar position. As a group their fans are less obnoxious when they come here, but the arrogance of the organization and some of their players about “The Cardinal Way” is annoying, and some of the spats with LaRussa, Molina, et al, have added fuel to the rivalry. I would put it at Cubs 70%, Cardinals 25%, and 5% for teams that may have a special place for smaller segments of the fan base, like people who live farther north and west and have a lot of interaction with fans of the Twins, who the Brewers still play every year.