If cop brutality is/was such a big issue with African American athletes...?

Then why were only African American NFL players protesting? Why weren't African American pro athletes in OTHER sports - baseball, basketball, hockey, golf, etc.- protesting? I am not trolling. I am just curious about this. I'm African American, and more importantly I am a Christian. I thank God I never had any real serious problem dealing with ANY American police officers. Please help- thank you.