A "youngsters party" which police said went "a little wrong" ended when two officers were hurt breaking up a fight.
Five people were also arrested in the brawl in Melton Mowbray's High Street on Saturday night.
Oakham Police tweeted it had "all gone a little wrong in #Melton youngsters party", adding "cops from all over" had been called in.
A special constable and a full-time officer were both hurt but their injuries were not serious.
Leicestershire Police Chief Constable Simon Cole tweeted that the attack on the officer was "#unacceptable".
Police said a "private under 18s" party had been held nearby.
The special constable injured her shoulder while trying to make an arrest in the fight, which broke out at about 23:10 GMT. The other officer hurt his wrist.
A 19-year-old girl was arrested on suspicion of assaulting an officer, two 17-year-old boys and a 16-year-old were arrested suspicion of breaching public order and a 17-year-old boy was arrested on suspicion of assault.
All have been bailed or dealt with by way of "a community resolution", police said.