Preston Crown Court was told John Harvey junior, 25, claimed father John Harvey senior had inflicted years of physical abuse on him - facts accepted by prosecutors in the case.
Sporting a crucifix and blazer jacket, he looked straight ahead as barristers revealed none of the family members wanted to make a statement about the incident, which happened at an address in Penwortham on New Year’s Eve.
At around 3.30am police received an emergency call from his mother and when they attended they found Mr Harvey senior lying at the foot of the stairs.
The court heard there was blood on the staircase.
The man had suffered a deep facial wound and his son was arrested on suspicion of assault when he told them: “I’ll admit I hit the c**t - I want the c**t to admit what he did to me.”
The older man told officers if he was “10 years younger I’d have battered him”.
Harvey, of Howick Cross Lane, Penwortham, admitted causing actual bodily harm.
Prosecuting Steven Swift said: “He pleaded guilty on the basis that he returned home and his father attacked him at the top of the stairs. He was not responsible for the lacerations - they were caused when he fell.
“Despite his injuries, he continued to be aggressive. The defendant admits punching him beyond reasonable self defence.
“He was angry at the aggression and the physical abuse he and other members of his family had suffered over many years.”
Judge Simon Newell was told a 12-year-old girl had witnessed the attack.
After struggling at the top of the stairs, Mr Harvey senior began to go downstairs but fell halfway. He suffered a scalp haematoma and fractured nose.
The defendant punched him at least 20 times.
Jacob Dyer, defending, said: “I appreciate there are aggravating features because the complainant was badly injured and a child was present.