Absolutely disgusting. Zero self-control, and he's VERY LUCKY he missed there because he could've seriously injured Plumlee with that punch. Ridiculous to see something like this from a young player.
He's a thug and I hope the coaching staff noticed this and is trying to put a stop to it right now. Absolutely unacceptable. Since he's not Cousins or Artest, people are going to try and pretend that it's no big deal, but anyway you want to spin it Valanciunas maliciously tried to hurt another player on this play.