England's Football Association have condemned Millwall fans for booing as players from their team and Derby County took a knee before their Championship match.
The second-tier game was among the first matches to see a return of supporters to stadiums since the start of Britain's COVID-19 restrictions in March.
Players throughout English football have been taking a knee since July, initially in support of the Black Lives Matter movement, although both the Premier League and the Football League (EFL) have since said the gesture is now linked to their own anti-racism campaigns.
Video footage of the start of the game contained loud booing from the 2,000 fans inside Millwall's 'The Den' stadium as the players took the knee.
In response, the FA said in a statement: "The FA supports all players and staff that wish to take a stand against discrimination in a respectful manner, which includes taking of the knee, and strongly condemns the behaviours of any spectators that actively voice their opposition to such activities."
Anti-discrimination body Kick It Out echoed the FA's comments, saying on Twitter: "We are saddened by the behaviour of the fans booing the players taking the knee today at Millwall.
"What this demonstrates is that players are right to continue standing up to discrimination, whether that is through taking the knee or speaking out," the body's chairman Sanjay Bhandari added in the post.
"The fight for racial equality continues and we will continue to work closely with clubs across the country to tackle discrimination in all its forms. We applaud the players for taking a stand and defying the hate shown today."
On Saturday (AEDT), Millwall players had released a statement saying:
"As a squad we are fully supportive of the entire football family's efforts in ridding the sport, and society generally, of all forms of discrimination.
"The gesture of taking the knee before matches provides an opportunity for us to do exactly that and continues to allow all those playing to publicly showcase their support - on behalf of the whole squad - for the fight against discrimination.
"We wish to make clear that taking the knee, for us, is in no way representative of any agreement with political messaging or ideology.
"It is purely about tackling discrimination, as has been the case throughout.
"We will continue to do this until the start of the New Year when a new and comprehensive anti-discrimination strategy will be announced by the club."
The controversy overshadowed Wayne Rooney's first win in interim charge of Derby as his team won 1-0 with a Jason Knight strike.