I think there's no uncertainty about whether this is a crime - it's "battery," which usually means hitting someone but can mean any "offensive touching." In practice, a "touching" that doesn't actually injure the person touched is virtually never going to be an issue, but this may be one of the rare cases where it does get prosecuted.

Technically, Missouri calls this "assault in the third degree" but it's the same as what is usually called "battery." Missouri's law makes it a misdemeanor to "knowingly cause physical contact with another person knowing the other person will regard the contact as offensive or provocative." ("Provocative" here probably means provoking a fight.) Seems reasonable to expect that a man should "know" that women might find hugs from a strange guy "offensive."

Given that we're only talking about hugs, there may be uncertainty over whether to prosecute him, but if there's reason to think he's a creep and not just a harmless hugger, I think they could prosecute him under this law if necessary.