The 25-year-old punched one man up to 20 times and left a 16-year-old boy with broken teeth, Liverpool Crown Court was told.
Barton, cousin Nadine Wilson, 27, and brother Andrew Barton, 20, were captured on CCTV in a number of violent incidents in Liverpool city centre on December 27 last year, reports ESPN.
At around 5am the footballer, who had consumed 10 pints of lager and five bottles of lager, went into a McDonald's restaurant with his brother and Wilson. The court heard Wilson became involved in a confrontation with a group of youths and the row continued outside the restaurant, with Barton caught on CCTV knocking an unidentified man to the ground.
He then straddled the man, and punched him four or five times as Wilson threw food at the victim before Barton punched him up to 15 times more.
Minutes later, the player attacked 16-year-old Jordan Spencer, punching him in the mistaken belief the youth had slapped Wilson. The punch broke a number of Mr Spencer's teeth.
Ian Harris, prosecuting, described the incident as 'violent and cowardly'.