Donald Trump slammed NFL players who have kneeled in protest of the national anthem during a speech in Alabama on Friday night.

Last year, quarterback Colin Kaepernick refused to stand for the anthem to protest against racial injustice and police brutality in the USA.

He has since been joined by others who have taken a knee or raised a fist during the anthem.

Trump also mocked efforts by the NFL to make the game safer, saying American football had become soft.