I doubt there would be enough evidence to convict a charge of common assault. Clearly the pillocks behaviour was provocative, in that it was causing distress to other passengers in that they were being delayed and also the fact the pillock was using loud and abusive behaviour and language.
The assistance provided by "the big man" could be deemed as appropriate in order to quell the situation. Removing said person from the situation requires physical contact if they are refusing to move and continuing to be a disturbance to other passengers.
Said pillock could also have gone quietly but chose to escalate the matter by using reciprocal and disproportionate physical contact, which again required an escalation of the response from the big man, which was not - from the video at least - grossly disproportionate to the situation in which they found themselves in.
If he had gone on to the platform and kicked his head in, that would have been disproportionate and would have been an assault. Merely using physical force to prevent re-boarding of the train isn't really and I would think (hope) that the PF's office will also see it that way, given the reaction of the public who witnessed the matter.
The prat got what he deserved and big man should be thanked for his services to the public.
