United States Vice President Mike Pence walked out of a National Football League game on Sunday, after some players knelt during the national anthem. Sportspeople across the country have been kneeling during the anthem as a form of demonstration that began last year in silent protest against police violence towards racial minorities.

Pence was attending a game in his home state of Indiana between the Indianapolis Colts and the San Francisco 49ers. When the national anthem was played before the game began, some 49ers knelt while some Colts, their arms locked, wore black T-shirts with the words “We Will” on the front and “Stand for equality, justice, unity, respect, dialogue, opportunity” on the back.

“I left today’s Colts game because President [Donald] Trump and I will not dignify any event that disrespects our soldiers, our flag, or our national anthem,” Pence said in a statement issued by the White House. He later defended his stand in a series of posts on Twitter.

Critics began to question whether Pence had only attended the game in order to make a stance by leaving, pointing out that he flew from Las Vegas on Saturday and was then going to fly to California on Sunday evening, Reuters reported.

But his office brushed off these claims. Pence had planned for “several weeks” to attend Sunday’s Colts game, where former quarterback Peyton Manning was being honoured, Reuters quoted an official as saying. “As he had discussed with the president, when several 49ers players disrespected the flag and the Nation Anthem, the vice president decided to leave,” the official said.

President Donald Trump tweeted in support of Pence on Sunday.

NFL spokesman Brian McCarthy declined to comment.

Less than an hour after issuing Pence’s statement, the White House released a picture of him and his wife at the stadium where the game took place, standing with hands over their hearts during the performance of the national anthem.

Trump’s criticism of the NFL players has played well with his conservative base while he grapples with controversies over Iran and North Korea, an investigation of Russian meddling in the 2016 election and policy struggles in Congress.