Here's how I see it.
Sparring - Essentially training, that's what it is. Training to develop ones abilities by going against another person. It's to help further abilities, or test abilities, whatever. Helping another person get better at one thing, so....Yeah.
Hard core sparring (Also could be called a fight) - A hard core sparring match is giving it all you've got, pretty much the same as going into a fight without the killing intent, or more so trying to kill each other. Take a look at Kenta vs Takara, they used electricity, slammed each other through trees, slammed each other on their heads....Pretty much a fight minus the killing. Which is what I think David wants, but that isn't very fun when one of those people are a million times stronger and can turn the tide in just a second...Which would be Rio vs Nohime. Obviously Rio would kick her ass, even if she lowered herself she could turn the fight around simply just by wanting to...No fun when only one character struggles.
Fight - Pretty much the same as above, without the whole friendly thing attached. Either you fight out of fucking anger or you fight to kill each other, that's really all there is to it. No explanation, fight is a fight
