Joseph Sharp junior wanted a lift to see his dying sister in hospital on September 16, 2015, but when his elderly dad refused, he became upset and pushed the old man to the floor.
The fall caused the 77-year-old to fracture his hip, setting off a chain of events that led to his death 17 days later from pneumonia.
Sharp, who was originally accused of causing grievous bodily harm and suffers from an anxiety disorder, was later charged with manslaughter and pleaded guilty just before a trial on March 1.
But despite the gravity of the charge, the 46-year-old of Short Stocks was handed a an 18-month suspended sentence and 100 hours of community service at Northampton Crown Court on Friday (March 17).
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Judge Rupert Mayo said: “This is a tragic case and one which is highly unusual.
“So unusual that the counsel prosecuting and defending this case have been unable to find something that is anywhere near similar.”
Prosecutor Stephen Kemp said that, back in September 16, 2015, Sharp had allowed his 77-year-old father to come and stay with him at his flat in Short Stocks.
But the relationship was fraught with tension at that time, the court heard.
Sharp junior had been subject to various physical abuses from his “mercurial” father growing up, but had decided to let the elderly man stay at his home.
On September 16 he had pleaded with his father, the only driver in the family, to take him to see his sister at hospital. She was in a coma at the time and has since passed away.
The court heard that Sharp became upset after being refused the lift and was captured on CCTV first “throwing a small dog” out of the way and pushing his father over outside the flat, before immediately helping him up.
The prosecution case centred around the fact Sharp knew his father used a walking stick and was frail when he assaulted him.
But, defending for him, Steven Evans said the 46-year-old could not have known of the consequences and said it could not be compared to other so called “one-punch” manslaughter cases, because the defendant showed minimal aggression.
Psychologists’ reports also backed up how Sharp’s anxiety disorder and learning difficulties would have impaired his decision-making ability at the time.
Mr Evans, said: “This is an unusual case of manslaughter, which should be seen and dealt with on its own particular facts.
“This defendant must have had no idea about the consequences.
“He has suffered himself as a result of what happened.”
Sharp’s clean record was also a factor in mitigation.
The 46-year-old had volunteered with charities, helped out at the local food bank and raised money for Macmillian Cancer Care by cycling around Silverstone racing circuit.