The Library of Congress has lots of pictures from the earlier part of the 20th century available for free online. Take this picture of Red Sox “Royal Rooters” during the 1910s:
(Click the picture for a bigger view)
As you can see, everybody has a hat on, they are all white men, they are waving pennants, wearing suits, and generally looking old-timey. Although there is one guy on the right who seems to be making a finger-pistol at us.
I wonder what would happen if a group dressed like this showed up at Fenway today…