Look, we are all sports fans. And I would bet we all get heated watching games. There have been times I yelled curses to make a sailor blush while watching TV, although in person (remember those days?) I rarely used anything stronger than damn. But no matter how I loathed, say, James Harden, I never screamed the n word. And he wouldn't hear me!
What I am trying to say is that we should, even when heated, drunk, whatever, have a line we don't cross.
It's possible Leonard was ignorant but I have to ask why. He's a grown man, an educated person, he needn't be a historian to have some awareness.