The 83-year-old was taken to hospital after the firework went off at around 3.20pm today (Wednesday) at a house in Stovin Gardens, Darnall, Sheffield.
His injuries are not thought to be life-threatening and police are now appealing for witnesses to come forward in their search for the suspects.
Sgt Phil Ackerley, investigating officer at South Yorkshire Police, said: “An investigation is now underway to identify those involved in this incident and I’d like to ask anyone who saw what happened to contact us.
“If you saw anyone acting suspiciously in the area this afternoon, or have any information, please contact police on 101 or speak to one of our PCSOs in the area.
“This type of behaviour will not be tolerated and I want to reassure local residents that anyone found to be using fireworks in a dangerous or antisocial way will be dealt with accordingly.”
Anyone with information is asked to call police on 101 quoting incident number 711 of 26 October 2016.
Information can also be given anonymously to Crimestoppers on 0800 555111.