Richard Roberts was walking home after babysitting his niece when a teenager was shot twice on the street in front of him.
The former Army captain, who last used his first aid skills in Afghanistan, managed to stem the blood loss and save the teenager's life.
He says children in schools should be having basic first aid training as standard.
The attack happened at 10:30 at night while the victim was riding a bicycle. The perpetrators were grouped around a car.
It's not the first time we've heard about military techniques being used to treat victims of stabbings and shootings.
In April Gavin Williamson, who was Defence Secretary at the time, said a pen developed on the battlefield filled with a blood clotting drug could be put in schools community centres and carried by police officers and forst responders.
The victim was shot twice in the shin and thigh but he survived, not least because of Richard's informed actions.