A 14-year-old boy died after being hit on the head with a hockey stick, an inquest heard.
Luke Hobson was injured as about 20 boys practised hitting balls before a training session at Blueharts Hockey Club in Hitchin on 28 March 2019.
Hertfordshire Coroner's Court heard the pitch lights were not on and there were no coaches supervising at the time.
Luke's parents said they were "disappointed and angry" with police and council investigations.
The inquest heard initial police inquiries were unable to determine exactly how Luke's injuries occurred until the boy responsible came forward.
In a statement, the boy said he was "trying to hit the ball up into the air" when he struck Luke.
"I didn't know Luke was behind me," he said.
"I ran to get first aid...I didn't mean to hit anybody. It was an accident and I am very sorry it happened."
The boy said he had not spoken up initially as he had "only later been able to fully remember details".
Luke's parents, Helen Moss and Peter Hobson, said investigations carried out by North Hertfordshire District Council and Hertfordshire Police had shown a "disappointing level of analysis, accuracy and conclusions".
The court heard Luke was taken by air ambulance to hospital but his injuries were "unsurvivable".
There was evidence of a "blunt force traumatic impact", a "skull base fracture" extending towards the brain stem and blood within the skull, Dr Curtis Offiah said.
Mr Hobson told the inquest that the pain of his son's death "does not fade".
"How can it be possible to have dropped him off for training as usual and three hours later for him to be dead?" he said.
"The vacuum he has left behind is as empty as ever...without Luke it is hard to find meaning in anything."
The court heard there are now locks on the gates at the hockey club and no-one is allowed to practise before sessions begin.
The inquest continues.