The 25-year-old was foundguilty by a jury of eight men and four women on 17.01.13 in Guildford Crown Court in Surrey, South East England, over an incident which took place at a Shell garage on Woodbridge Road in the same town on February 28, 2011.
Dappy and three accomplices - Kalonji David Stewart, Kieran Vassell and Alfred Miller - are said to have tried to impress Grace Cochran and Serena Burton, who were both then 18, by "chatting them up", Grace told the jury.
However, Dappy - real name Costadinos Contostavlos - turned nasty when the girls called him "boring" and proceeded to call them "sl*ts" and "ugly" as well as spit at them.
As his spit missed their persons, Dappy was cleared of two charges of common assault towards them.
Onlooker David Jenkins then intervened and told the men to leave the teenagers alone, to which Dappy responded to by spitting at him and putting him in a headlock and punching him.
This spitting, which hit Mr. Jenkins, makes up the charge of assault by beating. During the trial DNA testing proved that the saliva found on Mr. Jenkins` shirt was the musicians, with forensic scientist Carolyn Smith saying it would be "one in a billion" chance of it not being his.
Dappy was cleared of charges stating he struck two other males at the scene, who had joined in to help.
Saliva was found on David`s shirt, to which forensic scientist Carolyn Smith explained : "We estimated the probability of getting this DNA profile from another person who was unrelated to Mr. Contostavlos as one in a billion."
Kalonji David Stewart and Kieran Vassell were also both charged with affray.
Alfred Miller pleaded guilty to affray and he is awaiting his sentence.