One teenager has admitted the murder of 26-year-old Peter Cairns on June 11, 2021, on the Silkin Way footpath near Stonebridge Close in Telford, and will be dealt with separately.
But another three are in the dock at Stafford Crown Court accused of the murder of Mr Cairns and of assault occasioning actual bodily harm to his friend, Kaine Bushell. They deny all the charges.
None of the accused teenagers can be identified for legal reasons.
"The science doesn't help us with how the blood got there," said Adrian Keeling QC, defending the third of three teenagers who have been jointly charged with Mr Cairns' murder. "There is no evidence of what he did.
"It could be explained by proximity. One explanation is that something went into the blood and there has been a transfer on to the sword."
The trial has heard that there were no injuries on Mr Cairns that could be attributed to the sword which had been drawn after another defendant had said "show him the thing" in response to being stared at by Mr Bushell and told to walk on.
"The prosecution can't say it made contact and can't say it caused injury to Mr Cairns," said Mr Keeling.
Mr Keeling told the jury there is evidence that Mr Cairns had already been fatally wounded by stabbing with a knife before his client reached the scene and he could not have participated in the murder.
His client admits striking Kaine Bushell and causing him harm. But Mr Keeling said this had been on his back which was a "moderately safe part of the body, with a blunt object and had caused a bruise".
His client claims to have acted in self defence with Mr Bushell and of trying to stop the attack on Mr Cairns by getting between him and his attacker.
Mr Keeling told the jury that this is "not a murder case" against his client.
"At the highest it is manslaughter and assault but you cannot even be sure of these allegations," said Mr Keeling.
The young man was the only one of the three to stand in the witness box and be cross-examined, and his barrister said he had showed "courage".
"It would be tough for anyone but especially if you are only 16 years old after the events of a year ago. A year might be a long time," he said. He had been 15 years old when the events of the fatal day unfolded.
Mr Keeling said: "Fifteen-year-olds do not always think like adults. The teenage brain does not always think like an adult's brain does. They do not always think with clarity and logic."
Mr Keeling went through a series of decisions his client had made, including why he had joined a gang, why he had used an ornamental knife to play fight with a friend, and why he had chosen a blunt Samurai sword to take from Woodside towards Brookside.
"He did not stop and think," he said.
Mr Keeling added that the word "gang" is an emotive word, but it can be many things. His client had posed under a Brookside side making hand gestures.
He asked the jury to consider that the young man he was representing was showing "young and immature" behaviour, and was "sometimes a bit of a berk".
Mr Keeling said the young man could be considered of good character despite one single caution, when he pushed a police officer at the age of 13.
The incident could be seen in a positive light because it showed he did not act with a hair trigger to violence, as the prosecution claimed, the barrister said.
Of the young man's decision to join his friends on the fateful walk when they came across the two victims, Mr Keeling said: "It was stupid beyond belief but he was not spoiling for a fight."
The nature of the Samurai sword he chose to put down his trousers and carry towards the Castlefields underpass off Rough Park Way was that "it was never made to act as a weapon. It was already broken. It had no cutting edge and had "never been sharpened", he added.
"It was in effect a narrow metal bar, rather than a sword."
He said that there was no evidence it had cut anyone, but it had left a bruise on Mr Bushell's back.
It had been taken because it was big and intimidating and could be used to scare, and even to "put violence down", he said.
"If he knew violence was going to happen he would not want to take it. He would have taken something other than this Samurai sword," he said.
The defendant claims not to have offered help to Mr Cairns because he had been unaware of him being badly wounded. The court heard that Mr Cairns had been in the process of getting up after the attack and had been found 50 yards further away.
Trial judge Lord Justice Spencer is to start his summing up on Friday.
The trial continues.