Allegations of racism 

The alleged planned boycott against Jackie Robinson is vigorously denied by the interviewees in "The Spirit of St. Louis: A History Of The St. Louis Cardinals And Browns" by Peter Golenbock.  I am noting this very briefly.  As a baseball team in a former slave state, and having the reputation of being full of hillbillies (see:  Dizzy Dean, Enos "Country" Slaughter, etc.), it was going to be easy for people to convince themselves that the Cards would react badly to Jackie Robinson whether or not there was any further evidence of such.