Today, he admitted a charge of common assault in the Christchurch District Court where defence counsel Anselm Williams sought a discharge without conviction.
Vassalini also offered to make an emotional harm payment to the complainant.
Police took a neutral position on the discharge application, saying Vassalini was otherwise of good character.
The police summary of facts says the group began drawing attention after boarding the Western Line train to west Auckland about 5.40pm.
After a scuffle broke out, Vassalini shoved the male teen, causing him to lose his balance and fall against the side of the train. Vassalini's head also "collided with the victim's face", the court heard.
The victim was dazed and received a sore and swollen lip.
Vassalini later spoke to police and admitted pushing the teen as described but denied that he intended to strike him with his head.
When Vassalini became aware that an incident had occurred, he came forward and helped police with their inquiries, Judge David Saunders said.
He noted it was the lowest level of assault charge brought under Criminal Procedure Act and that Vassalini, who was not the prime offender, had offered to pay emotional harm compensation.
Judge Saunders said he was satisfied that a conviction would out of all proportion to the gravity of offending and granted the discharge without conviction.
He ordered Vassalini to pay the victim $750 in emotional harm compensation within seven days.
A 31-year-old Waikato painter and decorator was also charged and will be sentenced for indecent exposure in the Hamilton District Court on December 4.
A 35-year-old teacher from Papamoa, near Tauranga, is yet to enter a plea to a charge of assault with intent to injure and will be back in the Auckland District Court on February 5.
