Donald Trump’s attack on the National Football League Friday might have seem to come out of nowhere to some fans, but in reality, his disgruntlement with the NFL has a long history.

Trump, in a three-minute tirade, encouraged owners to fire players who kneel during the U.S. national anthem. The comments resulted in dozens of additional players taking a knee during the anthem, a closing of the ranks among NFL owners to stand against Trump’s remarks, and some teams not coming out onto the field for the anthem at all.

Read more at Fortune.com: Donald Trump’s War with the NFL Goes back 40 years