That's BS. Abusing your power? If anything you were doing good with it. Having a guy that childish and with those kind of anger problems is not what they need. I hope you explained and I hope they're smart enough to hire someone like you back. & along with hiring you back they should get you a bundle of fcking roses and take you for a fabulous dinner for even questioning their decision in promoting you. Just sayin.

Holy shit balls! Sounds like a crazy place. Lay a complaint with the police for the assault and then lay a complaint with employment tribunal. **** them all back up!

Take a picture of the mark, file a complaint, go to HR.

Do you have natural justice rules in employee management in the UK? I.e. Where you have to tell them they are facing termination, provide their story, reasons why they think they shouldn't be fired, a consideration of their prior conduct (recorded conduct & only things that have been discussed w the employee) and then a decision by an unbiased party? Unless your company had less than 15 employees, in Australia that would be a potentially unfair dismissal if you didn't follow process. Even if it was also declared a valid decision. Hope you find a better job soon.

Sounds like you had logical reasons for firing them, violence in the work place should not ever be tolerated, especially for that stupid of a reason

Was anyone there to witness the incident?

if that's their sole reason for firing you, sue

Appeal on the grounds of unfair dismissal. Also, if your workplace has CCTV, get a copy of the incident as evidence.

Did you take the right steps in firing him?

I would have filed two sets of charges