United States President Donald Trump has been quite vocal over the past few weeks about footballers protesting during the national anthem, which began last year as a symbolic protest about police violence against racial minorities.

This time, Mr Trump weighed in following a walkout by Vice President Mike Pence on a National Football League game in his home state of Indiana after some players knelt during the national anthem.

But why is this issue being given so much attention? ABC News spoke to the USSC's academic director Dr David Smith and research associate John Barron about the issue.