I think it's far more fundamental than that, a fighter is a mentality a refusal to be beaten, until your actually beaten and even then,
if someone has that attribute they take it into all aspects of their lives, even if they never actually punch someone at all or regularly.
I see it often in professional sport, that when things are going against a team, players all over the pitch stop trying, if they have fighters in their team, you can spot them easily, some times they have enough to turn a match around, usually they dont as fighters are a rare commodity and worth a considerable amount of money in professional sport and business.
if you want to turn that to the subject of professional fighters, most have it or they dont last long as professionals and certainly never achieve much with out it.
on the slightly less obvious subject of dojo sparring, you can get a long way with iut it coz the sparing is commonly water down, so having to dig deep isn't a regular occurance