The victims, who are friends, were a part of a "heavily intoxicated" group playing an arcade game at the pub, Judge Sygrove told New Plymouth District Court on Friday.
Not far from the group was Adams, who was having a drink with a mate at a bar leaner.
Around 11.40pm, a duty manager approached the "slightly raucous" group and unplugged the gaming machine.
This resulted in one of the victims becoming argumentative and racially abusive towards the staffer.
He was asked to leave the premises and as he was being escorted out, his abuse continued.
At this point, Adams took it upon himself to get involved and began to accost the man.
A scuffle broke out, which included the other victim, and all parties were throwing punches.
Once they were separated, the victim who was asked to leave continued to be ushered outside.
Meanwhile, Adams followed the other victim to a table and swung a right hook to the man's chin, which immediately knocked him out.
Adams then left the bar and was met by the evicted victim who called on him for a fight.
Taking on the challenge, Adams approached the man and threw a single punch. The victim was immediately knocked out and hit his head on the footpath.
He spent several days in intensive care at Taranaki Base Hospital with a subdural haematoma and facial fractures.
His road to recovery continues and he and his wife have had to give up their work as contract milkers as a result of the head injury.
The couple had to move out of their farmhouse and have lost about $50,000 of income and $20,000 of rental income.
The other victim sustained significant swelling from the attack and suffers ongoing emotional and relationship issues.
Judge Sygrove had difficulty reading the victim impact statements, describing the content as "heart-rendering".
The victims' lives had changed irrevocably, he said at the sentencing of Adams.
"[One victim] was severely handicapped for some time and remains quite handicapped in a number of ways."
Judge Sygrove admonished Adams' violent behaviour, describing his actions as "unbelievably bad".
But said he was an otherwise "worthwhile member of society" with fulltime employment as a builder, and a supportive family.
"It shows you the danger of alcohol and youth. And it's happening all the time in our society," Judge Sygrove said.
Police argued the offending was premeditated and vigilante behaviour, while Defence said it was provoked and impulsive.
When sentencing Adams, Judge Sygrove took into account his youth, remorse, rehabilitation efforts and his willingness to attend restorative justice, which did not go ahead.
On admitted charges of injuring with reckless disregard and injuring which would have led to manslaughter if death occurred, Adams was sentenced to eight months' home detention.
He was also ordered to pay $1500 reparation to one victim and $500 to the other.
