President Donald Trump criticized NFL players who knelt during the national anthem during preseason games on Thursday, while receiving support from Colin Kaepernick.

“The NFL players are at it again – taking a knee when they should be standing proudly for the National Anthem,” he wrote on Twitter on Friday.

During a game against the Tampa Bay Buccaneers, Miami Dolphins players Kenny Stills and Albert Wilson knelt at Thursday night’s game, while another Dolphins player, Robert Quinn, raised his fist during the playing of the anthem, according to HuffPost. 

“When I’m on a knee, most of the time I’m praying, and thank God for having Albert next to me. Being a part of this protest hasn’t been easy. I thought I was going to be by myself out there,” Stills told ESPN. Adding that he and Wilson did not plan the protest together.

“Today I had an angel with me with Albert being out there. I’m grateful he sees what’s happening, and he wants to do something about it as well.”

In May, NFL Commissioner Roger Goodell announced a policy that would require players to stand during the playing of the national anthem when they’re on the field, giving them the option to remain in the locker rooms.

The policy was placed on hold last month while the League and the Players Association work on a resolution.

Former San Francisco quarterback Colin Kaepernick showed his support for Stills and Wilson online Thursday.

“My brother [Stills] continued his protest of systemic oppression tonight by taking a knee. Albert Wilson joined him in protest. Stay strong brothers!,” Kaepernick wrote.

Kaepernick began kneeling while the anthem played during the NFL’s 2016 season to protest what he felt was unjust treatment Black people in the U.S. faced from law enforcement.

The silent protest spread throughout the league and Kaepernick has remained unsigned following the end of 2016 season.

He’s currently suing the NFL stating that the owners have colluded against him to keep him out of the League.

Wilson told The Palm Beach Post that he knelt during the “Star-Spangled Banner” because of recent violent events that took place near his hometown of Port St. Lucie, Florida.

“It’s just something that’s been heavy on my heart, heavy on my mind,” he said. “Just two incidents in my city that happened. I’m pretty much the biggest thing in my city, so I have a chance to take a stance on it.”