An inmate in Lincoln prison died after he was knocked to the floor by a single punch during a row in the showers, a jury heard.
Emmanuel Dos Santos, 43, is alleged to have unlawfully killed fellow prisoner Samuel Harrison, 29, following the argument on B wing.
Mr Harrison was found with a serious head injury on September 11, 2017, and died two weeks later in hospital.
Dos Santos denies a charge of manslaughter and claims he was acting in self defence, a jury at Lincoln Crown Court heard.
Jon Dee, prosecuting, described the case as a “classic” one punch manslaughter.
“On September 11, 2017 Mr Dos Santos punched Samuel Harrison,” Mr Dee told the jury.
“That blow would not have killed him. Mr Harrison, as a result of that punch, fell back.
“When he fell back he hit his head on the floor, that is what killed him.”
Mr Dee said the prosecution did not claim that Dos Santos intended to kill or seriously injure Mr Harrison.
“He did an unlawful act,” Mr Dee alleged. “He punched him and that ultimately caused his death.
“The only issue is whether the punch was lawful. Mr Dos Santos says he was acting in self defence.”
The jury heard both men were serving prisoners on B wing.
Mr Dee said the build up to the incident was caught on CCTV outside the third floor shower block.
“Mr Dos Santos is considerably more muscular, broadly built, than Mr Harrison,” Mr Dee said.
“There is clearly some discussion, as we see in the video Mr Dos Santos encourages Mr Harrison to go with him.”
Mr Dee said there is a gap of around 30 seconds before Dos Santos could be seen leaving the shower area on his own.
The prosecution allege another inmate heard a verbal exchange between the two prisoners and witnessed a punch to Mr Harrison which knocked him backwards.
Mr Dee said a second prisoner in the showers overheard someone say “why were you banging last night?”
It is claimed the prisoner looked out to see Dos Santos grabbing Mr Harrison by his clothing.
He then heard someone reply “I wasn’t banging,” and looked away before hearing a loud noise.
“There was an argument but Mr Harrison was no threat. Mr Dos Santos did not have to resort to violence,” Mr Dee claimed.
It was intially thought that Mr Harrison may have suffered a drug related seizure and he died in hospital on September 25 last year.
Dos Santos was interviewed a day after the incident. Mr Dee told the jury Dos Santos admitted speaking to Mr Harrison about the gym but said he was under the influence of drugs and fell to the floor.
“Ultimately he was saying the fall was nothing to do with him,” Mr Dee added.
The trial continues.