Plessy vs Ferguson was a Supreme Court case that upheld the doctrine of "separate but equal." The tension began when a man named Homer Adolph Plessy was traveling by train from New Orleans to Covington, LA and refused to ride on the "colored" railway coach.
The Plessy vs Ferguson case allowed African Americans to now have a baseball team, but this team was kept separate from the "white" team. This ruling was upheld until the Brown vs. Board of Education case which decided that separate, but equal, is still inherently unequal.