In cases of domestic abuse, which trumps best, the law, or the code of the shield?

Thinking back to this question and this link Largest Street Gang in America, provided by @incendiary_dan. I get the strong impression that cops have no compunction of sticking up for their pals behind the shield even if skirting or obliterating the law. The question came to mind, if a cop is beating his wife, who can she turn too? If she calls 911 because he is chasing her around the house with a fireplace tool, his buddies are going to be the one to show up. Had it been you or I we would leave that night in handcuffs, especially if we had laid one cm on her. What if the cop not only chased her with it but struck her three to five times leaving obvious bruising? What would happen, would he go to jail, would they bust her, would they make her leave? If he was taken away would he be released after he calmed down and would never have been booked? Seeing cops don’t want to bust cops, if one viciously attacked his wife or G/F who does she call?