The stark image is typical of As It Is, a DVD based on real testimonies of gang members in Glasgow's Easterhouse estate. It is designed to be used in classrooms and youth groups with children as young as 10. The film - a result of work between Glasgow-based production company Autonomi, community groups, and Strathclyde Police - aims to dissuade young people from gang-fighting, but allows CCTV recordings to speak for themselves.
The footage portrays, not the airbrushed, choreographed violence of Hollywood, but the ugly, lurching violence of the street. It is intercut with young people explaining why gang-fighting appeals; the film-makers eschew the type of moralising voiceover that washes over sceptical youngsters.
"If there's loads of youse and there's loads of them, and you're all getting chased down the lane or whatever, it gets the adrenaline goin' and a' that," says one boy.
"It makes you feel good if people are scared of you," says another.
But most interviewees show no relish; they are softly spoken and matter-of-fact. A girl of about 13 says: "If you're fighting with another lassie who's carrying a blade, then obviously she's going to try and stab you. There's always something about anyway - like glass and a' that - so you can just pick it up and hit them with it."
The little bravado on display in the 15-minute film quickly elides into regret and sombre reflection.
"It's like an addiction - that's exactly what it is, an addiction," says one boy of his involvement.
An adult former gang member says: "People still want to get me. It's going to be like that for the rest of my life because of my teenage years of gang-fighting."
There is a chilling coda to the CCTV footage: a prone body is repeatedly kicked and punched by a blur of around six assailants.
Then the after-effects of violence are seen: there is lingering footage of an attack victim in hospital with a grisly laceration between his thumb and forefinger and a gaping wound on his shoulder.
Gordon Shaw, headteacher at Lochend Community High in Easterhouse, believes the film is "unprecedented" in its depiction of gang violence, which has left rooms of youngsters in stunned silence. "There hasn't really been anything as graphic and hard-hitting as that," he says. "I think that's really been a major source of the impact. I was concerned that it might glorify with the bravado you see, but that quickly fades and you begin to see the consequences of the actions."
Mr Shaw believes the film can also help staff understand the issues better. "Teachers find it very difficult to comprehend," he says. "Most of us come into school in the morning and leave at the end of the day, but the youngsters here are facing very challenging circumstances in the evenings - their brothers, sisters and even parents might be involved in territorial activity."
Jimmy Wilson, of community project Family Action, in Rogerfield and Easterhouse, helped persuade young people to be interviewed for the film. It took a year for filmmakers to gain trust and get their remarkably open interviews, and he describes the results as "unheard of".
Mr Wilson believes the film provides a short, sharp shock, but will have little longer term use unless it is part of intensive work lasting several weeks. He says territorialism and gangs became deep-rooted in Easterhouse after poor town planning in the 1950s left the huge new estate with few amenities and employers.
Many gang members are following in the footsteps of parents, siblings and even grandparents, but Mr Wilson says only about 5 per cent of Easterhouse's young people are in gangs. Even they do not necessarily think of themselves as being in a gang - to them it is just a group of friends, and only their rivals are in gangs. "These young people, many of them come from broken homes where they have family that potentially are using substances," says Mr Wilson. "They use gang membership as a substitute family."
He stresses that Easterhouse is being revived, thanks to police and community projects and new jobs at the Glasgow Fort shopping centre. But if that does not steer young people away from gangs, the testimony of Hugh Burns at the end of As It Is might.
His son, 13-year-old Hugh Jnr, died fleeing a gang fight in 1996, and he has advice for young viewers: "Imagine how your mum or dad would feel when they go into your room each day and they're hoping to still see you. They can still smell your clothes, and they can still sense you in the house, but you're not there."