Jordan Rowley 20, watched the “nasty and sustained attack” with a camera - yelling “go on, lad” and “f****** wasteman” as a mother walked by with her three young children.
Prosecutor Lynne Bickley described how the injured youth was left “distressed and heavily bleeding” following the Boythorpe Avenue attack on October 18 last year.
The court heard the traumatised victim now carried a self-defence alarm at all times and struggled to eat due to jaw damage.
Ms Bickley said Rowley, who admitted assault by beating, had acted in joint enterprise by filming the incident.
The youth he filmed beating the other teen - who cannot be identified - had already been sentenced at another court.
Prosecutor Ms Bickley said: “A local resident was walking with her children - her 10-year-old son, 8-year-old daughter and 10-month-old daughter.
“She was pushing a pushchair when saw a group of teenage children - two of them had phones and were laughing and pointing while filming.
“She could see (the victim) was clearly distressed and bleeding heavily - she helped him call his mother and allowed him to come home with her.”
Rowley’s solicitor Clare James said her client had never met the injured boy before.
Ms James said Rowley - diagnosed with ADHD, anxiety and depression - made full admissions in police custody and accepted he made a “stupid decision”.
A Magistrate told him: “This was a very nasty, vicious assault and you could have stopped it - you didn’t even know the young person who was being assaulted.
“You were as much to blame. Young children witnessed it - it’s very serious.”
Trainee sous chef Rowley, of Kingsclere Walk, Birdholme, was handed a three-year restraining order, a 12-month community order with 15 rehabilitation days and a mental health programme requirement.
He was ordered to carry out 100 hours unpaid work and pay £100 compensation, £85 court costs and a £95 victim surcharge.