A West Yorkshire Police officer who punched a violent prisoner after he racially abused and assaulted his partner - also a fellow police officer - said "anyone in the same situation would have done the same".
PC Robert Dovey is currently the subject of a misconduct hearing and is alleged to have punched the prisoner several times before deliberately putting him in the back of his van so he could "give him a good hiding" on the way to police custody.
The hearing, which is taking place at the force's headquarters in Wakefield, heard how PC Dovey had been called to reports a man was being violent and abusive towards officers - one of whom was his partner - during an incident in Horbury on December 9, 2017.
Police officers at the scene described seeing PC Dovey punch the man several times in the face, while a police sergeant alleged that PC Dovey wanted to pull over while transporting the prisoner to the police station and "give him a good hiding".
PC Dovey, who has been an officer with the force since 2004, denies the allegations.
Giving evidence about transferring the prisoner to his van, he said a struggle took place in which the man tried to bite and hit him, which resulted in him issuing a single punch in self-defence.
PC Dovey said: "My belief was that he was going to injure me, I believed he wanted to bite me.
"My use of force was proportionate in the circumstances. This was someone that could have caused me serious injury. My behaviour was extremely reasonable given the circumstances and it was necessary.
"Anyone in that situation would have done the same as what I did.
"I did not cause him any injury.
"He was aggressive and shouting abuse at me and the other officers. He was foaming at the mouth and he was a difficult individual to deal with.
PC Dovey said he remained professional and calm throughout the whole incident.
He said: "I acted within my powers as a professional police officer. I did not let human nature take over."
The panel heard how PC Dovey's partner had been left scarred for life by a violent man six months prior to this incident and had only just returned to full duties.
He admitted saying to a colleague, Sergeant Graham Dent, while transporting the prisoner to the police station, that this incident "could finish her off", but denied wanting to stop the van to give (the prisoner) a good hiding.
PC Dovey said: "I said more than once that he deserved a good hiding, that is how I was feeling as I could not believe what he had done to the other officers. I admit it was not professional or rational but that was a difficult incident to deal with.
"I never once contemplated stopped the vehicle to assault him."
PC Dovey's account was described by Matthew Holdcroft from the appropriate authority as an "entire fabrication".
Mr Holdcroft said PC Dovey had no injuries despite saying he was involved in a violent struggle with the prisoner and stated that his main thought on the day was not for his job but for his partner.
Mr Holdcroft said: "You got into the back of that van because you thought he deserved a beating and you were in the course of giving it to him when the other officers pulled you off. There was no justification for the force you used."
PC Dovey is alleged to have breached the Standards of Professional Standards in relation to Use of Force, Authority Respect and Courtesy and Discreditable Conduct.
It is alleged he used force that was not deemed reasonable, necessary or proportionate on a member of the public who had been detained by other officers.
It is also alleged that the officer moved the member of the public into another van to give the officer the opportunity to assault him further during the transfer and during the journey.
The hearing has been adjourned until Thursday.