PC Josie Bower had been at a birthday party at a golf club in Clayton, Bradford with her partner and a group of friends before the group headed to The Sun pub to continue the celebrations on the night of August 24, last year.
When they got to the pub, PC Bower's partner, who is employed as a PCSO for the Yorkshire force, headed to the toilets with two other members and it was there the police officer witnessed her kiss the other woman.
A misconduct hearing, held earlier today, heard how PC Bower, who was in the next cubicle, leaned over and pulled the woman's hair after witnessing the kiss, causing her to fall over, before walking out of the toilets.
As a result she was ejected from the pub by security staff.
Temporary Detective Inspector Carl Morrison said: "The complainant was outside the pub waiting to leave when PC Bower's mother pointed to her.
"The next thing she recalls is waking up on the floor, however three witnesses described how PC Bower had walked up to her and struck her in the face.
"CCTV footage gathered between 2.45am and 3am on August 25, 2018, shows PC Bower walk towards the group and punch the complainant in the face. She then falls to the floor and does not move. PC Bower then tries to get to her on the floor before being moved on by other people at the scene."
The woman was taken to hospital for CT scans after complaining of headaches.
PC Bower, who was arrested at the scene, was interviewed by officers but gave a 'no comment' response throughout.
She was charged with common assault and appeared at Barnsley Magistrates Court for trial on May 20, this year.
She was found guilty of the offence and given a two year restraining order, as well as an 18 month community order.
She was also ordered to pay £500 in compensation, an £85 victim surcharge and £75 court costs.
The misconduct panel heard how PC Bower had been in a "tumultuous" relationship with the complainant since February 2014.
DI Morrison said: "The appropriate authority believes this is case of domestic abuse."
In mitigation for PC Bower, Police Sergeant Chris Bentley said the police officer had acted in self defence and that it was her who had been a victim of domestic abuse and coercive control at the hands of her partner.
He said the complainant had previously been observed acting in a violent manner to PC Bower on nights out and had been physically aggressive.
Sgt Bentley said: "There has been a continued pattern of violence which has caused PC Bower to be on edge and feel on edge all the time.
"This incident was not pre-meditated or a sustained attack.
"PC Bower has glowing character references, her colleagues still trust her and say she is a valuable member of the team having worked for West Yorkshire Police since December 2014."
When asked by Chief Constable John Robins why she hadn't reported the domestic abuse she alleged she had suffered, PC Bower said: "When you are in something like that you don't see it until you are out of the situation."
PC Bower said she had "only wanted to speak to her partner" and "wanted to find out why" she had kissed another woman.
She said her partner's friends had been intimidating the whole evening and she had only acted in self defence.
"When I did approach her, all her friends were shouting abuse at me," she said.
PC Bower admitted her behaviour had breached the Standards of Professional Behaviour in relation to Discreditable Conduct and that this amounted to gross misconduct.
Chief Constable John Robins said he could not say whether PC Bower was a victim of domestic abuse or coercive behaviour but said he did not accept she was acting in self-defence.
He said: "PC Bower determinedly without provocation hit the complainant so hard it rendered her unconscious.
"We see events like this happen all the time and as a force we are trying to prevent them in our One Punch campaign.
"I can say most definitely, without any hesitation, that PC Bower must seize to be a police officer without delay."
PC Bower was dismissed from the force without notice.