The recent flashpoint of Colin Kaepernick taking a knee renews a long tradition of athlete-activists speaking out against racism, injustice, and oppression. Like Kaepernick, Jackie Robinson, Paul Robeson, Muhammad Ali, Bill Russell, Tommie Smith, and John Carlos--among many others, of all races, male and female, pro and amateur--all made the choice to take a side to command public awareness and attention rather than "shut up and play," as O. J...