Fans of Millwall, who in the past gained a reputation for violence, revel in their unpopularity. Before the game, the topic of players taking a knee was discussed on Millwall's fans forum and the first-team squad said in a statement on the club's website they supported efforts to end 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 added. "It is purely about tackling discrimination, as has been the case throughout."
The Football Association issued a statement after the match, which Derby won 1-0, saying it supported players' right to protest.
"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," a spokesman said.
Derby coach, former England international Wayne Rooney, was also upset at the reaction the players received from the stands.
"To hear that is very disappointing and upsetting for a lot of people," Rooney said.
"I'm pleased with how my team dealt with that. They've had to put that to the back of their minds for the 90 minutes but I'm sure it's something they were thinking about."
Millwall fans were blasted on social media for their response. British media personality Piers Morgan was among the critics, but saved special praise for Derby star Colin Kazim Richards, who stood and raised his fist in opposition to the people booing.
Richards himself spoke out after the game. "Having to say this is a pain but I'll say it every single damn time this is why I STAND and STAND PROUD and I have to say every single person involved with @dcfcofficial did too, made me proud to wear this shirt with the boys today!!! Absolute disgrace," he tweeted.
Actor Reece Dinsdale said on Twitter the booing was "disgraceful", while UK politician Angela Rayner slammed the "disgusting scenes".
Journalist Henry Winter called it "embarrassing from those Millwall fans" while cricket writer Barney Ronay added: "Those people at Millwall booing the players for taking the knee are an embarrassment to the club, south London, football and the rest of the modern world. @MillwallFC needs to make this very clear.
"People won't have the same politics and agree about everything. But booing that moment is a racist act."
Former Manchester City defender Micah Richards told the BBC: "It is just disheartening. How do these fans get allocated to the games?"
