Colin Kaepernick has come under intense scrutiny over the past month due to his decision to first sit, and then take a knee during the National Anthem. He began his silent demonstration in protest of the treatment of people of color in America. In particular, he has repeatedly pointed to the issue of treatment of African Americans by police.
Kaepernick has had support for his actions, but there has been intense vitriol in response to his protest. Some people have a problem with his method of protest, while others have a problem with a black man demonstrating against social injustice in America (or at least are uncomfortable when these demonstrations occur).