A nan suffered a head injury and a fractured wrist after she grabbed her granddaughter's partner while the couple were rowing.
Kevin Bowden "shrugged" 71-year-old Barbara Gahan to the floor during an altercation with Lisa Reynolds.
He claimed the argument was sparked by Ms Reynolds refusing to give him the keys to his home.
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Liverpool Crown Court today heard a dispute broke out at Ms Reynolds' Wirral home on March 27 of this year.
John Williams, prosecuting, said Merseyside Police sent officers to the New Ferry property at around 11pm following a 999 call.
He said Bowden had been drinking before going to bed, with the row erupting when he returned downstairs.
Bowden admitted assault occasioning actual bodily harm against Ms Gahan and his basis of plea, which was accepted by the court, was read out.
In it, he said: "I asked Lisa for my flat keys and my phone but she refused to tell me where they were."
He said an argument broke out between the pair, who were separated by a kitchen table, and as things got heated Ms Gahan "grabbed me from behind". He said he "forcefully shrugged" off the pensioner.
Ms Gahan was injured as she banged her head as she fell. She was also left with a wrist fracture.
In his summary of the case, Recorder Andrew McLoughlin said: "It would appear from your own admissions that you had been drinking heavily. There was an altercation with your then partner. No charge followed from that. But then, most regrettably and in my judgement quite seriously, you involved yourself in an altercation with Barbara Gahan."
The judge continued: "In essence, Barbara Gahan approached you from behind because you were involved in an altercation with her relative, your then partner. In the unseemly nature of this altercation, you unlawfully assaulted her."
The court heard there was no victim personal statement from Ms Gahan because she had since died. Her death was was not connected to this incident.
Bowden, a dad-of-three of Beckwith Street in Birkenhead, had 14 convictions for 24 offences. His record included recent short jail sentences linked to assaults in a pub and a hotel.
Andrew McInnes, defending, said the "penny had dropped" for his client, who realised that alcohol was behind many of those incidents.
He added: "He is aware how bad the facts of this case sound. Ms Gahan was his partner's grandmother, a lady he was fond of and had significant contact with and, in drink, he has to accept he caused injury to a woman who intervened in a row between him and his partner."
Judge McLoughlin concluded: "In my judgement, this is sufficiently serious given it was a violent assault on a 71-year-old lady that it merits a custodial sentence."
He sentenced the 46-year-old to eight months in jail.
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