As Gary said earlier, this is Ballmer we are talking about here. Doc probably went to the owner (as he should) after DeAndre called him.
Doc: "Look, we have a situation here. I just got off the phone with DJ. He wishes he hadn't agreed to sign with the Mavs. He says he felt pressured by his mom, plus all of the teams needed an answer so they could make their plans, and he just blurted an answer. Now he wants to stay with us."
Ballmer: "Can he change his mind?"
Doc: "Well, people don't do that. There's a grace period involved, so technically I guess he could, be we wouldn't accept it, because it isn't..."
[Baller's face begins to inflate and turn red.]
Ballmer: "CAN HE CHANGE HIS MIND?"
Doc: "Yes, I guess, but it's not something that people do...no other team will want to trade with us, and..."
[Ballmer slaps the table hard]
Ballmer: "You head to the airport and take my plane to wherever that bastard is, and you say whatever it takes to get him to change his mind. Call up everyone else who you can call, too...call Blake in Hawaii."
Doc: "Okay, I'm going. But Cuban and the Mavericks are going to show up, too. And Fegan. It might get ugly."
Ballmer: "Fegan! That bastard. Take my gun. He gives you any grief, shoot him in the leg. I'll take care of it with the cops."
Doc: "But..."
Ballmer: "GO!"