A man has been convicted of murdering a kickboxer with a sword at a party.
Leam Smith, 19, claimed he "leapt to the defence" of a friend who was in dispute with Dainius Kasiliauskis, 27, when he attacked him with the weapon in Peterborough on 12 June.
But a Cambridge Crown Court jury found Smith, of Branston Rise, Peterborough, guilty of murder.
His friend, Alvaro Vilhete, 30, of no fixed address, was convicted of grievous bodily harm with intent.
The trial heard Mr Kasiliauskis, known as Danny, was a regular user of drugs and at the address in Tilton Court had been refused them by Vilhete.
Prosecutor Stuart Trimmer QC told jurors Lithuanian national Mr Kasiliauskis then punched Vilhete, who subsequently produced a hammer and struck him with it.
A woman at the party then produced a sword "in an attempt to calm things down", Mr Trimmer said.
The prosecutor said Smith took the weapon and used it with an action "described as a chopping motion".
Father-of-three Mr Kasiliauskis died from a fatal stab wound to the chest, jurors heard.
The court heard that the majority of Mr Kasiliauskis' Facebook posts related to professional fighting and Smith had "liked" two of those posts.
This led to a "solid and safe inference that Leam Smith knew full well that Danny was a trained fighter", said Smith's defence barrister, Lisa Wilding QC.
She told jurors Smith took the sword "because he thought it was necessary to stop the assault that was happening".
"It had unplanned, unintended fatal consequences, but everyone reacts differently," she added.
While jurors convicted Smith of murder, Vilhete was cleared of that charge.
The pair will be sentenced at a later date.
In a tribute, Mr Kasiliauskis's family called him "a courageous person who would never shy away from a challenge".
"His passion for boxing made him an inspiration to his friends, family and people he didn't even know," the tribute said.
"From coaching children to helping people as a personal trainer, there's nothing he wouldn't have done to help the people in his community."