CS spray was fired on a crowd in a Derby street during a fight which left a police officer in hospital with leg and head injuries.
The incident happened as a group of peaceful protesters opposed to violence in Gaza marched through Normanton following a 100-strong vigil in the city centre on Saturday.
Police say violence erupted in Pear Tree Road, Normanton, at about 2.30pm, after the protesters were joined by a group of youths, who began walking with them.
A Derbyshire police spokesman said: "Some of these youths became aggressive, resulting in a fight breaking out.
"Police used CS spray to restore order."
The police officer who was hurt has been now been released from hospital.
The officer, who suffered an injured knee and a minor head injury, was discharged after being treated for his wounds.
One man, a 32-year-old from Derby, was arrested after the incident on suspicion of assault. He was bailed yesterday pending further inquiries.
The incident led to the Derby Caribbean carnival parade from Pear Tree being delayed and arriving about an hour later than scheduled in Derby's Market Place at 4pm.
Earlier, the pro-Palestinian marchers, who said they were "like-minded people from the community showing solidarity with Palestine over the problems in Gaza with Israel", had gathered on the steps of the Council House in torrential rain.
Their action followed the worsening military situation in the Middle East involving Israel and Palestinians.
A number of speakers talked of the situation in Gaza and urged people to sign a petition, calling for peace.
This is to be presented to Derby MPs Chris Williamson and Margaret Beckett.
One man spoke of his parents who are living in Gaza and told how they live in fear.
The protesters spent more than an hour outside the Council House before deciding to walk to Normanton.
Witnesses to the CS spray incident, or anyone with information on the people responsible for the trouble, should call Derbyshire police on 101 or Crimestoppers, free and anonymously, on 0800 555 111.
