A stepfather looking for two stolen bikes was murdered by a 16-year-old boy armed with a cricket bat, a jury has heard.

Derek Whyteside, 42, suffered a skull fracture due to a single blow from behind and then collapsed to the ground, where he was attacked by two men, Stafford crown court was told on Tuesday.

Opening the crown’s case against the 16-year-old, prosecutor Kevin Hegarty QC alleged that Whyteside was hit with a full swing of the bat after the teenager “crept up behind him” on the afternoon of 18 June this year.

Hegarty told the jury that the victim, who lived with his partner and her four children, was attacked by the boy after going to Malinslee in Telford, Shropshire.

The barrister said: “He was struck across the back of the head with a bat. The impact fractured his skull and the fracture extended into his right eye socket. Before he could take another step, he then collapsed on the ground.”

Whyteside’s head struck the ground as he landed, Hegarty alleged, causing him another fracture, and he died two days later.

During his opening speech to the jury, Hegarty said of the defendant, who cannot be named because of his age, that he “intended at the very least to do really serious harm to Derek Whyteside. He did so from behind … without Mr Whyteside even seeing him. He gave Derek Whyteside no chance to take any action to defend himself.”

The teenager, who denies a single charge of murder, was arrested and told police he had acted in self-defence, later claiming to have been defending his mother, the court heard.

Alleging that the boy had intended to cause really serious harm, making him guilty of murder, Hegarty told the court: “This is not a case of self-defence … He wasn’t under any attack from Derek Whyteside – he wasn’t even looking at him.”

The jury heard that William Owens and Gareth Owens, who are not on trial after admitting affray, both struck the victim while he was on the ground.

The charge admitted by William Owens, 41, and Gareth Owens, 39, both of Telford, states that they “used or threatened unlawful violence” at the scene of the attack on Whyteside.

Jurors were told that Whyteside was seen carrying a knuckle-duster as he looked for the children’s bicycles, which had been taken from outside his home in the nearby town of Dawley earlier the same day.

Whyteside’s partner, Michelle Beddall, told the court she went to the 16-year-old’s home to speak to his mother after viewing a neighbour’s CCTV footage of the bike theft.

Beddall, who works as a carer, told jurors the boy laughed after she spoke to him about the bikes, while his mother claimed the youth in the footage was not her son.

In her evidence from the witness box, Beddall added that she had later phoned Whyteside and could hear him saying, “Just leave the bikes,” before several further calls to him went unanswered.

Under cross-examination from the 16-year-old’s barrister, Patrick Harrington QC, Beddall said her partner had been carrying a knuckle-duster to protect himself, having been given the item by a friend.

Harrington asked what she had meant by a social media message saying the thieves “stole from the wrong people this time”. Beddall responded: “I wasn’t going to let it lie. I was going to go to the house and get my bikes back.”

The trial continues.