A 26-year-old man was hit with what is believed to be a rounders bat by a balaclava-wearing attacker in Grantham.
The assault happened in New Street between 6.30pm and 6.50 pm on Wednesday.
The victim was approached by two men, both wearing dark clothing and balaclavas, and one of them hit him on the arm.
He was not seriously hurt.
One of the offenders is described as around 5ft 10in tall and slim and the other about 6ft 2in tall and stocky.
Police are appealing for anyone who may have seen these men in the area at the time of the incident to get in touch as soon as possible.
Anyone with information should call 101 or Crimestoppers anonymously on 0800 555 111.