Thirty young people were seen fighting in McDonald's East Lancashire.
The police took part in Rawtenstall yesterday afternoon at 15:15 p.m.
Haslingden Road injured a man in a fast food restaurant.
Police spokeswoman said: "About 40 youngsters are fighting McDonald's Rawtenstall restaurant and surrounding areas and, as a result, a man is being investigated as he is injured.
"We can keep in mind that all parents need to know about their own children coming out of the house."
In February, a police officer was summoned by Rawtenstall McDonald's three nights over a night to report teenage struggles and abuse.
McDonald has contacted the commentator. If you have information about all the affected people, contact the police officer 101.