Police were pelted with chairs, cans, rocks and flares late on Tuesday by some of the hundreds who attended a protest in the southern English coast city of Southampton, where Henry Nowak was killed in December.
Two people were arrested and 11 officers and a police dog were injured, police said.
Nowak's death has triggered debates about policing and knife crime and has spurred claims by far-right activists and politicians that there is bias against white people in the justice system.
Nowak's killer, Vickrum Digwa, who is Sikh, falsely claimed he was the victim of a racist assault by 18-year-old Nowak, who was white.
When police officers arrived, they initially treated the wounded man as a suspect before noticing his injury and trying to resuscitate him.
Prime Minister Keir Starmer said on Wednesday that the case had left "serious questions to answer, including how accusations of racism informed police thinking".
But he called the street violence "disgraceful and completely unacceptable".
Home Secretary Shabana Mahmood said Nowak's family had "made a powerful call to us all yesterday to not let Henry's death be used to create further division, hatred or tension.
"There can be no justification for hijacking this tragedy to stir up violence and disorder. Those responsible can expect to face the full force of the law," she said.
Digwa, 23, was convicted of murder and sentenced Monday to life in prison with a minimum term of 21 years.
The judge said he did not believe Nowak had said anything racist to his attacker.
After the sentencing, police released video showing officers dismissing Nowak when he told them he had been stabbed and repeatedly said he could not breathe.
The Independent Office for Police Conduct is probing the actions of the officers from the Hampshire and Isle of Wight Constabulary, and the National Police Chiefs Council will review its anti-racism guidance.
After the sentencing hearing, the victim's father, Mark Nowak, said the case was not about racism or religion, and that he wanted his son's death to lead to safer streets and not to be used to create "further division, hatred or tension".
But Nigel Farage, leader of the anti-immigration Reform UK party, said on Tuesday that it was an example of so-called two-tier policing - a popular far-right talking point that claims ethnic minorities are better treated than white people.
Farage urged people to respond to the incident with "pure cold rage", and said, "white lives matter just as much as Black lives".
X owner Elon Musk and British far-right activist Stephen Yaxley-Lennon, known as Tommy Robinson, have also expressed outrage at the crime.
Hampshire Police chief constable Alexis Boon said he understood the "desire for answers and accountability" but that should not be used as an excuse to attack police and "bring violence to our streets".
