Police said between 40 and 50 people were at the scene in Thompson Park, Burnley, Lancashire at about 1330 GMT.
Mohammed Shafiq, 50, from York Street, Nelson, Lancashire, who was described as a "family man", died on Tuesday night at the Royal Blackburn Hospital.
A 17-year-old and an 18-year-old man have been arrested. Police said their inquiry was in the "very early stages".
'Family man'
Det Supt Mick Gradwell: "This is a very serious incident in Thompson Park.
"I appeal for anyone with information, or who may have seen this incident to come forward.
"A 50-year-old man has died after it appears he intervened in an incident.
"He was a family man.
"We are actively seeking others in connection with the stabbing."
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