So Garou speed blitz.
He scales to Post-Superfight Genos, who scales above
Mach 42.3. Also, the scaling chain has multiple blitzes before this point. Mach 29 is the speed value of chapter 1 Genos, who's capable of blitzing his chapter 1 self several times over. So yeah this is a speed stomp.
Going on the assumption you'll equalize speed.
There isn't a single thing Izuku has that can land a blow on Garou. He's vastly more skilled in CQC that it's not even funny, his ability to redirect attacks would work on anything Izuku can use. The only thing Izuku might be able to hit on Garou would be a surprise large AOE attack from his shockwaves.
But that'd only work once at best, any other attempts would be redirected with WSRSF.
However, Izuku isn't dumb and will very quickly realize he stands no chance against Garou up close. Meaning he'll begin keeping his distance and attack Garou at range instead with Air Force, Blackwhip, and any thrown objects he can grab. Although, I don't think any of this can put Garou down.
He can dodge or redirect any of Izuku's ranged attacks, I don't see any of that hitting him. Blackwhip is worthless against Garou due to the LS difference alone.
Assuming speed equalization. Izuku cannot take Garou down from range, I literally cannot see how he could. I don't know how Garou's stamina is against things that aren't wearing him down. But with whatever his Reactive Evolution do, fighting Garou in a prologued battle is always a bad thing.
He'll eventually reach a point where Izuku will be vastly slower than him and his attacks can be effortlessly dodged.
So I'm pretty Izuku can, at best, delay an inevitable outcome.
Not certain how fair this is even when though I'm giving Izuku the benefit of the doubt here. I don't see what he has that can even take Garou out. It's not even a case of him having something he can use but he doesn't use it quickly enough in character. Izuku could be bloodlusted and I still don't see him landing a single hit on Garou.
The difference in their skill and abilities is just too great. Honestly, I don't think Izuku vs Garou can ever work at all.
Although, right now this is a speed blitz/stomp.