Police and paramedics were called to Street Lane in Roundhay at around 1.15pm today.
Officers have sealed off Adi’s barber shop near the junction with Talbot Road.
A 32-year-old man was treated at the scene for facial injuries, before being taken to hospital.
His injuries are not believed to be life-threatening, police said.
A spokeswoman said: “Enquiries are at an early stage and are continuing. Anyone with any information is asked to speak to Leeds Police via 101, quoting 0767 of Aug 5.”