Champion trainer Evan Williams, 55, believed 72-year-old Martin Dandridge was a rabbit-hunting intruder after seeing him in one of his fields wearing a head torch and with a dog.
Williams told the court armed poachers had threatened him with a shotgun just weeks before the attack and said they would burn down his barn.
The “anxious” trainer armed himself with a hockey stick and repeatedly swung it “forcibly” towards holidaymaker Mr Danbridge breaking his arm.
Mr Danbridge had been staying in a nearby holiday cottage to be close to his daughter who had recently given birth and was walking his dog Gulliver when he was set upon.
Prosecutor William Bebb said: “The defendant used a weapon to inflict violence and there were repeated blows.”
Mr Bebb had previously told the court: “It was a dark night and Mr Dandridge went to walk the dog before going to bed – at around 9.30pm with a head torch and the dog also had a light attached to his collar.”
“Two policemen were also nearby and on duty that night monitoring rural crime such as lamping and poaching.
“Mr Williams drove up to the police in his 4×4 and said to the officers ‘they are lamping in my field and we’re going to challenge them'”.
Williams shouted at Mr Dandridge “what are you doing in my field with a lamp and a dog?” before attacking him on December 4, 2024.
Mr Bebb said: “Mr Williams rained down blows from the hockey stick on Mr Dandridge.
“This was a man out walking his dog and now being assaulted with a hockey stick.”
Cardiff Crown Court heard Mr Dandridge, from Swindon, Wilts., was found to have suffered two fractured bones in his arm.
Minutes before the attack Williams and his son-in-law – jockey Connor Ring – had chanced upon two police officers investigating rural crime and the officers followed him to the field in Llancarfan, Vale of Glamorgan and witnessed the attack.
In a victim personal statement Mr Dandridge said he could no longer take part in his former hobbies such as golf, DIY and metal detecting due to ongoing pain in his arm.
He said: “The psychological impact of the assault is for me the most difficult part. I still struggle with anxiety, disturbed sleep and intrusive thoughts about what happened.
“The hardest part is remembering the moment I was going to die and realised there was nothing I could do about it. I vividly remember it.
“I struggle with the memory of being completely helpless and defenceless.”
Williams has more than 1,200 career winners including victory in the 2020 Welsh Grand National and scooped more than £3million prize money during the past five years,
Williams, whose full name is Richard Evan Rhys Williams, denied the single charge against him but was found guilty after a trial.
David Elias KC, defending, said Williams had a “deep love” of his family and horses and had been confronted by trespassers who threatened to “shoot” him and to burn down his farm six weeks before the incident.
Mr Elias said Williams’ attack “was driven by heightened fear, hypervigilance and a distorted threat perception.”
He said there had been an “unprecedented number of character references and testimonials” from more than 500 people.
Mr Elias said: “It is testament to the huge amount of feeling that is felt from so many people from all aspects of his life.”
Judge, recorder Angharad Price told Williams he had committed an “appalling offence” and Mr Dandridge was “still living with the effects of your actions 16 months ago.”
She said: “On that day you had a choice, you could have let the police officers you met on the lane attend the scene and respond to the emergency you felt there was. Instead you chose to respond yourself – urgently racing to the paddock.
“When you gave evidence at trial you talked very passionately of your passionate race horses and their sensitivity, you also talked strongly of protecting your family from harm.
“However that protection should not have come at Mr Dandridge’s cost – he should not have paid such a high price for walking his dog on the wrong field.
“It is never acceptable to take the law into your own hands. This sentence will be a lesson to you that it is always better to call the police if you think a crime is being committed.”
Williams was jailed for three years and told he must serve half the sentence behind bars.
