Provy definitely left his feet prior to contact, which is against the rules. So no, not clean.
He didn't really need to do that. Would have sent Barzal flying even if he stayed low.
Probably clean but cheap. That would be a penalty in the NFL. No need for Provorov to do that. Barzal could have easily been hurt bad or at the least a concussion. The NHL is trying to be more like the NFL and would like to avoid lawsuits as much as possible. Like hitting a defenseless Wide Receiver you'd think a hit like this would be banned.
Provy definitely left his feet prior to contact, which is against the rules. So no, not clean.
He didn't really need to do that. Would have sent Barzal flying even if he stayed low.