A British Transport Police officer suffered serious injuries to his ankle during an attack by a thug at Leeds railway station.
A court heard the officer had to undergo surgery after being punched and forced to the ground by a Josiah Lapompe.
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Lapompe was locked up for three years and one month after pleading guilty to causing grievous bodily harm.
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Leeds Crown Court was shown footage of the incident on September 3 last year as the station was busy with commuters.
Ashley Metcalfe, prosecuting, said the officer approached Lapompe after he had abused staff at a ticket desk at 6.30pm.
The 35-year-old told the officer he was trying to get to Peterborough but did not have any money or a ticket.
The officer told the defendant to leave but he turned and headed back towards the station.
CCTV cameras from the Wetherspoons pub showed Lapompe hitting the officer, knocking his helmet off.
The two men struggled then fell to the ground.
Lapompe was restrained when other officers and members of the public came to help.
Miss Metcalfe said the officer, aged in his twenties, had to have an operation after fracturing his ankle in three places.
He has been unable to return to work since the incident.
The officer said in a victim statement read to the court: "I am not sure what the future holds, which worries me greatly.
"I am not sure what kind of physical fitness I will get back to."
Lapompe later told a probation officer that the victim was lying about what had happened,
He told the officer that "God would take revenge" on him
Lapompe, of no fixed abode, has previous convictions for assaulting a police officer and abusing railway station staff.
On one occasion at London's King's Cross station he told a station worker: "I am a prince. I am going to chop your head off. Who do you think you are? You should be kneeling before me."
Kenton Sergeant, mitigating, said Lapompe had not intentionally caused the injuries to the officer during the incident..
Judge Tom Bayliss, QC, told Lapompe: "Just as he was protecting the public, so I as a judge, must protect the public.
"You have shown absolutely no remorse."