Trainer Evan Williams has been jailed for three years for attacking a dog walker who was on his land.
Williams, 55, repeatedly struck Martin Dandridge, 72, with a hockey stick during the assault.
Mr Dandridge, from Swindon, Wiltshire, suffered injuries including a fractured arm in the incident on Williams' land at Llancarfan, Vale of Glamorgan, south Wales, on the evening of December 4 2024.
The defendant denied a charge of causing grievous bodily harm with intent, but was convicted by a unanimous jury after 90 minutes of deliberations following a trial at Cardiff Crown Court in March.
On Tuesday, Recorder Angharad Price sentenced Williams to three years in prison.
She told Williams: "This is an appalling offence where you attacked Mr Dandridge causing him serious injuries.
"I know that you fully understand that he is still living with the impact of your actions on that day 16 months ago."
The judge told Williams that he had a "choice" on that day - to confront Mr Dandridge himself or wait for nearby police to attend.
"When you gave evidence at trial, you talked very passionately of your champion racehorses and their security, you talked of protecting them from harm," she said.
"You also talked about protecting your family from harm. However, that protection should not have came at Mr Dandridge's cost."
The judge described an incident that had taken place six weeks before the assault, in which Williams disturbed poachers on his land and was threatened with a shotgun.
"The earlier incident you experienced with threats of violence to you and your home must have been very frightening," the judge added.
"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 is a multiple Grade One-winning trainer who has had success at the Cheltenham Festival.
Last month Ask Brewster, running in the name of his wife, Cath, who had taken over the licence upon Williams being found guilty, won the Fulke Walwyn Kim Muir Handicap Chase at Cheltenham.
