As far as I know nobody's accused him of being a rapist--but it certainly seems like he was heavily abusing alcohol towards the end of his high school years and into early college. He was extremely evasive regarding his teenage drinking habits, and he seemed pretty damn nervous at mentions of both Mark Judge and questions on whether he'd ever suffered from blackouts or memory loss due to drinking.
I think it's entirely possible that 1) the event took place and Kavanaugh has zero memory of it, or 2) the event took place and Kavanaugh, in an inebriated state, went too far with roughhousing and didn't realize how aggressive his actions were.
The third and fourth possibilities--that one of Kavanaugh or Ford is knowingly lying about the assault--just don't seem likely. Ford first mentioned the event six years ago and came forward under immense duress here--she's faced death threats, for God's sake. On the flip side, Kavanaugh truly seems to have no recollection of either her or the event.
Either way, why appoint Kavanaugh to a lifetime SCOTUS position with this cloud over him? There are dozens of conservative judges out there with equally impressive credentials, all of whom could enter the SCOTUS unencumbered. What's the point of pushing forward a candidate with multiple assault accusations and a murky history? There's still time for another pick--Amy Barrett, for example, who seems like a great candidate--to go through.