Who is he? I know nothing about this guy
He's a G-Leaguer. Still young, 23. Did enough to get a call up last year with the Nets when the team caught the injury/covid bug during the bubble. He's an athletic rim running big who can catch the ball, dunk and rebound. He has a huge wingspan, about 7'5 (!). Don't expect anything else from Hall besides provide energy out there.
He hasn't played well in any of the G-League Ignite games, but you can see moments where his athleticism shines through.
Edit: Here's his highlight reel from last season.