I think NBA By-Laws have Moral Turpitude clauses that allow them to take this sort of action.
Apparently, the NBA Constitution has a requirement that franchise owners conduct business on a "reasonable" and "ethical" level.
The powers of the owners to terminate another the franchise of another owner are contained in Paragraph 13 of the NBA Constitution (which was adopted by the NBA owners on Oct. 26, 2005). The specific reasons for termination are for gambling and the like. There's a general termination right if an owner "fails to fulfill" a "contractual obligation" in "such a way as to affect the [NBA] or its members adversely."
The alleged failed contractual obligation would be Sterling's failure to conduct business on a "reasonable" and "ethical" level.
Not for this kind of behavior.