A man battered his disabled neighbour with a stick after believing he was responsible for drug dealing in the area.
David Reynolds got into a verbal altercation with fellow resident Terence Johnson outside his home in Linacre Road in Litherland.
The 40-year-old answered the door when Mr Johnson came to his flat, and claimed he thought the victim was carrying a knife, and was trying to enter his home.
Reynolds' dog also escaped but after initially acting in self-defence he later accepted his behaviour went beyond that.
Using the stick, he caused injuries to Mr Johnson's head and arms during an assault which continued after the victim fell over, Liverpool Crown Court heard.
The victim, 52, was found by police outside and taken to hospital.
Mr Johnson suffered a wound to his right temple, his right and left eyebrows, which required stitches, and a broken bone in his elbow.
He also had swelling to his left hand and discolouration to his right knee.
Fiona McNeill, prosecuting, told how the two men had a history of disagreements, before the incident on June 6.
Johnson, who has mobility issues and uses a walking stick, lives above Reynolds in a first floor flat, and said he had come to his neighbour's flat to "resolve outstanding differences" between them.
In a Victim Impact Statement, Mr Johnson described being traumatised by the incident, suffering from disturbed sleep, and needing to see a psychiatrist.
Reynolds has 24 convictions for 48 offences, dating back to 1995, including cases of assault, burglary, criminal damage and public disorder, Ms McNeill said.
Bernice Campbell, defending, said it was the victim who came to Reynolds' home, and started banging on the door.
Her client had gone to retrieve his puppy, and had suffered injuries, along with Mr Johnson, although not as severe.
The lawyer said: "He [Reynolds] is a kind considerate family man who has strong moral values."
Many complimentary references from neighbours, friends and the landlord who owns the Litherland flats, were handed up to Judge Andrew Menary, QC, the Recorder of Liverpool.
Reynolds, who admitted grievous bodily harm, has a grandchild who has severe autism, and helps his daughter bringing up that child, it was heard.
Ms Campbell added: "He has taken further education [courses], and wants to come out [of prison] and assist other people.
"This was a bad state of affairs, and not a horrible man attacking a vulnerable pensioner."
Reynolds wrote a letter of apology to the court.
The barrister said: "He wishes he'd not have gone out that day, but he followed his dog out as he felt the dog was in trouble.
Judge Menary, who said he was not going to adjudicate on the drug dealing claims, described the attack as "unpleasant", and added: "You [Reynolds] didn't go looking for trouble, it came looking for you."
And admonishing him for his lengthy criminal record, he said: "If you continue to behave in this way, you will get prison sentences and they will get longer and longer."
Reynolds was jailed for 18 months.
An application for a restraining order was turned down.
