A new documentary making its debut on Tuesday evening explores a mostly forgotten chapter of NFL history: 1946, when four African-American players broke the league’s color barrier – one year before Jackie Robinson famously did the same in Major League Baseball.

The documentary is called “Forgotten Four: the Integration of Pro Football,” and it focuses on the stories of Kenny Washington, Woody Strode, Marion Motley and Bill Willis. Ross Greenberg, a former president of HBO Sports who produced the documentary, sat down at the MoneyBeat desk this morning to talk about the this little-appreciated chapter of pro sports.

“No one has bothered to tell this story,” Mr. Greenberg said. “So I said, we’re telling the story through them, and their families.”