A man was taken to hospital with injuries to his head and arm after being assaulted in Rushden.
Police were called to Upper Queen Street in the town at about 1.30pm on Monday after reports a 40-year-old man had been attacked.
He suffered a head injury and broken arm in the incident, and was taken to Kettering General Hospital for treatment.
A police spokesman said a 25-year-old man had been arrested in connection with the incident, but had been released pending further enquiries.
The spokesman added a weapon was used in the incident, but was unable to confirm what it was.