Of course an accursed Cowboys fan, like yours truly, absolutely loved this piece on the racism of storied Redskins owner George Marshall:

Still, in the early days of professional football, with teams like the Kenosha Maroons and the Staten Island Stapletons--nearly fifty different squads in the 1920s, many of which were able to stay in business only a year or two--the very idea of a pro football league was mocked. Baseball was the national pastime, already inspiring writers like Ring Lardner; college football was beloved in the places where it still is today (Ann Arbor, South Bend), and many where it's now an afterthought (the Bronx, New Haven). Boxing and thoroughbred racing rounded out the big four spectator sports of the day. Professional football barely registered. 

It is largely for this reason that the NFL, in contrast to major league baseball, had actually had a few black players--the owners were desperate enough to accept them, and the public just didn't care enough to lodge the usual protests about "mongrelization." But in 1933, the league suddenly banned black players. It did so secretively, and no one would ever own up to the decision. 

For decades afterward, none of the game's celebrated founding owners--George Halas of Chicago, Tim Mara of New York, Art Rooney of Pittsburgh, Tex Schramm of Los Angeles--would ever admit that there'd been a pact. But somehow, black players disappeared. Smith, a professor at Nichols College in Massachusetts, interviewed several owners and writes that evidence points to Marshall as the ban's instigator. In a 1942 interview, Marshall argued that if black players were allowed to participate, Smith writes, "white players, especially those from the South, would go to extremes to physically disable them," so they were kept off the field in their own best interests.