Crown prosecutor William Slack said a struggle ensued, during which Tobler headbutted a 63-year-old man.
The other man tried to intervene and was thrown to the ground by Tobler.
Tobler then pinned the 63-year-old man to the ground before leaving.
His previous crimes included violence and drugs, such as a 2011 conviction for entering a man's house and holding a knife to his throat.
Tobler was also convicted in 2015 for assault occasioning bodily harm and common assault for an attack on a former partner.
He had already pleaded guilty prior to Thursday's sentence to two counts of common assault and a count of assault occasioning bodily harm.