Isn’t the nub of the problem here proportionality? If someone (male or female) is marching towards an intended target with a raised gun in their hand then a certain level of violence (whacking them on the back of the head with a chair for example) to prevent the shooting is justified – it’s the (probable) lesser of two evils. That’s not what happened though – the woman was walking behind a row of chairs and Field saw her, moved his chair back to block her, then assaulted her.
Might she have had a concealed weapon? Yes she might have done, but so might anyone in the street – that doesn’t give me the right to assault them though because I think they might be carrying heat.
What he should have done if he'd wanted to intervene reasonably was to have blocked her way, then either waited for security to arrive or walked toward her such that she would have been forced to retreat. In other words, acted proportionately.
I see by the way that Field claims to have acted “in the heat of the moment” as if that were some kind of defence or justification. It isn’t. Anyone can act in the heat of the moment, but they must expect to face the consequence when they do.
Short version: the guy’s a thug.