I don't know the statistics, but this is almost certainly a losing battle for Saitama. The main reason is because 1. She has vastly more hax, & 2. Ryuko has this kind of Regenerationn:
High-Mid: The ability to regenerate from being blown / cut to pieces, or from a small piece of your body, such as your severed head, a single organ, or a finger.
Although Saitama has demonstrated willingness & capability to dodge -like when fighting lower members of the House of Evolution- he is much less passionate. It could be argued Ryuko is a brute, but the same case could be made for Saitama.
I'd hesitantly put them equal in terms of skill, but not much else. We've never seen the full extent of Saitama's Stamina, but Ryuko has Very High Stamina.
Astonishingly, Ryuko may also beat Saitama in Lifting Strength, given her
At Least Class T to his
At Least Class G.
Class G: 10^9 to 10^12 kg (The mass of the human world population, the largest man-made structures)
Class T: 10^12 to 10^15 kg (The mass of the heaviest mountains)
So Saitama probably can't try to win through incapacitating her with stuff like pinning her under mountains of rubble, unless they make a game of piling it on top of her & her breaking it out to exhaust her; And that depends on Saitama's Unknown (As we've never seen the full extent of it.) Stamina being higher enough compared to hers he can keep it up.
Similarly, trying to suffocate or restraining hold her probably won't work either, nor will throwing her into space.
On the assumption his Stamina WOULD prove superior, he could try running away to exhaust her, but Ryuko has range via air shockwaves, her giant scissor blades, & outmaneuvers by having Flight. Other than Serious Strikes for shockwaves, he can't really fight back at range, & he can't fly.
And even if his Stamina IS better, running away to exhaust her is an uphill battle.
Finally, even if he CAN One Punch Ryuko.... Well, that's why I mentioned her High-Mid Regenerationn above. Again:
High-Mid: The ability to regenerate from being blown / cut to pieces, or from a small piece of your body, such as your severed head, a single organ, or a finger.
Leaving even more than pools of blood/life fibers/whatever left of her PROBABLY won't kill Ryuko, & she'll probably come back. Maybe a bit more fatigued from the assault & regenerating, but still a threat.
And even if he does put up a fight in a straight-up brawl?
Gains significant boosts to her Attack Potency and Durability the closer she is to dying,
All in all, even if she doesn't have the superior statistics, she might with that ability, & even if she doesn't, Ryuko outhaxes, outmaneuvers, might outskill, & even outlifts.
Even if Saitama kills her, she can Regenerate so long as she isn't just turned to blood & dust -hard to do that to someone on your own tier- & has even a small piece of herself left.
Given that he can't win probably via BFR (She outlifts him, so he can't bury her alive, she can fly & breathe in space so throwing her out of the atmosphere won't do much.), incapacitation (Superior lifting means a restraining hold or suffocating strangling probably aren't sustainable.), can outmaneuver him (So running until she collapses of exhaustion likely won't work, even if his stamina is better.) & probably can't keep her dead permanently....
....AND, again, she outclasses him in hax, & maybe skill....
I can't see a way Saitama can win this. At all. (Barring the minute possibility he can hit someone on his own tier, if not higher within it, hard enough to destroy her past a level Mid-High Regenerationn can bring her back from; Which means reducing her to mostly blood. Very sure that won't happen.)
With all that in mind,
I'd like to propose the possibility that this matchup is a Stomp by Ryuko against Saitama.