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The team's best defense is on their offense anyway so anyone who could protect the paint and hustle for the team is a good alternative. OgNasty already said Green doesn't have that same offensive threat so I think Capela is a decent replacement for Green.
I don't expect it to happen before the new season starts. It could be on the next trade window.
I cannot see the Warriors wanting to trade Green unless he gets pissed if they don't give him a max deal. While he is an asshole and a hothead, he also gets under players skin and throws off their game along with being a top tier defender. He's well worth keeping i'm just not sure he's worth max money.
Maybe still worth keeping him for the upcoming season but the next one will be a completely different story. His style of roughing up and trash talking opposing players may have worked in the past but I think it's becoming less and less effective.
He and his agent would likely push for a max contract. I don't think his ego would let him settle for less.
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Green hasn't been a great player for a long time now. I mean he was good by 2016 but since then he hasn't been as good as he used to be, those days when he had little points but a lot of rebounds and assists and played amazing on defence are long gone, he is bad at almost everything.
That's probably why he improved his trash talking game hehe.