I don't know, looking back, I've had sex with girls that were "above" my league in terms of looks. Only one girl that was a charity case and "below" my league in terms of looks. Most girls have pretty much been "above" my league in terms of looks. I've never really had like a legit sculpted six pack. Despite that, it's never really been an issue. For as long as you're not a moron and you have an attractive face that's not resting on an ugly body... I haven't found looks to be that much of a make or break factor (as a guy).
Obviously, if the guy is like below a 7-8 out of 10, then he really shouldn't be thinking about doing anything with a 9-10. But he doesn't have to be a 9-10 himself in terms of looks to do something with a 9-10.
I think a girl is out of a guy's league if he's like a whole 2-3 steps lower than her in terms of looks, and she is more socially dominant and assertive than he is, and she has substantially more motivation than him (for life activities, fun and entertainment), and she makes way more money than him, and she's way more accomplished than him.
I mean, if that's the case, I don't care how "nice" you are, it's just not gonna happen. And if it is gonna happen, you're no longer a man, you're like this pocket drag along puppy dog play thing for her own "emotional" gratification.
Basically, if a relationship with you is not mutually beneficial and rewarding, then you're out of her league.