Because the Cubs have lots of fans and because the northern Chicago suburbs pretty much stretch to Wisconsin, you get a lot of Cubs rooters in the stands when the Brewers host the Cubs at Miller Park. So much is this the case that Miller Park on such occasions is informally known as "Wrigley Field North."
The Brewers, understandably, don't much care for such encroachments by their NL Central rivals. "Well then," one might plausibly say to that. "Perhaps Brewers fans should buy more tickets."
Sound advice indeed, and the club is going to do its part to ensure that happens
Brewers apparently don't want Cubs fans to buy tickets from them
CBS Sports | Feb 9