Definitely Pratt Street before a game at Camden Yards. They finally stopped brewing in the basement of the late 1800s building, which is bad for tradition (it was an old Peter Austin system) but good for availability and the head brewer's back. They still open ferment in their new facility. Great British ales.
Union Craft and Waverly are two breweries right by each other near Hampden, maybe a 10 minute drive (or uber) from downtown. Union makes great beer. Waverly is new and can be hit or miss, but worth seeing if you're up there.
Also, check out Max's Taphouse in Fells Point. Even if they don't have any special rare events that weekend, there's always a great selection (and 120 taps).