No one has alleged that Sterling did not or has not “fulfilled his contract obligations” and I do not see any evidence of that.
Yes, I believe it is Article 35A (c) and/or (d) that he is alleged to have violated:
(c) Any person who gives, makes, issues, authorizes or
endorses any statement having, or designed to have, an effect prejudicial or detrimental to the best interests of basketball or of the Association or of a Member or its Team, shall be liable to a fine not exceeding $1,000,000 to be imposed by the Commissioner. The Member whose Owner, Officer, Manager, Coach or other employee has been so fined shall pay the amount of the fine should such person fail to
do so within ten (10) days of its imposition.
(d) The Commissioner shall have the power to suspend
for a definite or indefinite period, or to impose a fine not exceeding $1,000,000, or inflict both such suspension and fine upon any person who, in his opinion, shall have been guilty of conduct prejudicial or detrimental to the Association.
There is an 'ethical conduct in business dealings and contracts' clause that is vaguely worded and which is what they might try to get him with, the argument being that Sterling's comments were unethical and caused damage to the labor relationship between the NBA and the players. If the NBA pulls the trigger on that then it'll be the legal catfight to end all legal catfights. A media whore like Sterling would love it. And I suspect the NBA has no other choice than to try. Certain people will demand it.
At the end of the day I suspect that the NBA will have to be happy with the punishment they have given him. Sterling can be a sports mogul in name only. While the NBA cannot force him to sell they likely can appoint people to manage the team since Sterling can no longer hire or fire. Eventually Sterling will die and his heirs will get it.