If someone sees only half the story it's unfair to judge the security guard by what you saw. You might have missed the threatening, abusive, violence that preceded her being restrained. If she had been any of those things, I'd rather restrain a person like that as competently and as quickly as possible, if she looks like trying to defy your request for her to go away, than to go in half hearted and risk getting knifed, bottled (which happened in our an ASDA near us recently by a respectful owner of an ASBO) or worse.