Members of the public assisted an officer from Suffolk police as they were struggling to detain a "violent and aggressive" man.
The incident happened at 2.51pm on Saturday on Angel Hill in Bury St Edmunds, just outside the No. 5 restaurant.
Bury St Edmunds Police tweeted about the incident, saying: "Thank you to the brave members of the public on Angel Hill, Bury St. Edmunds this afternoon who came to the assistance of an officer struggling to detain a violent and aggressive male.
"Without your help, the officer could have been seriously injured.
One witness who saw the later part of the incident said: "From what I saw, a middle-aged man was shouting.
"All I saw was this guy on the ground with lots of the public on him, about six people.
"About a minute later a police van arrived. They literally ran at this guy and pulled off the public and arrested him. He looked quite distressed."
Bury St Edmunds Police released a second tweet, asking the people who helped out today to contact them.
"If you were one of those people who helped out on Angel Hill today, we would really like to hear from you. Please email CEOburystedmunds@suffolk.pnn.police.uk."
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