A 22-year-old man was verbally abused and assaulted while walking past the Halifax bank in Lower Street, Kettering.
The attacker walked out of the branch and started verbally abusing the victim as he walked past.
A police spokesman said: “The offender then assaulted the victim, by pushing him and then punching him in the face.
“The offender then walked off towards the clock tower.”
Police are appealing for witnesses to the attack which took place between 2.10pm and 2.20pm on Thursday, March 28.
The attacker was white, 20-years-old, 5ft 9in, of large build, had light ginger short hair and a spotty complexion.
He wore a black puffer jacket, blue jeans and trainers.
Witnesses to this incident, or anyone with information about it, can call Northamptonshire Police on 101 or information can be given anonymously to Crimestoppers on 0800 555111.