GSW had to release him to save on salary.
Celtics should pounce on this guy. He is very athletic, has power forward body who can play 5, has 3 point shot range, great shot blocker, only 22 years old. Much more upside than Poirier, who should be cut to make roster room. This guy was the 8th pick in the 2016 draft, probably the best athlete from that draft (per Fran F). He has under-performed, but the Warrior brass actually liked him and did not want to release him.
Grab him before someone else does, Danny.