I don't live in Oakland, I live nearby. My ladyfriend is born and raised in the "O" (still lives there) and the following is roughly what she said to me.
Before Quan was elected in a controversial race (rank choice voting) Oakland had hired Anthony Batts to be its police Chief (2009). Batts was considered something of a superstar, he was welcomed as a choice by much of the community. He was seen as a reformer who wanted to change the culture of the department. Obviously the Oakland PD has a checkered past.
Shortly before Occupy started, Batts resigned. The perception among many is that he was pushed out by Quan, who wanted to install her own choice, Howard Jordan. It's clear that Batts' timing was calculated to annoy her, it came right before some fancy law enforcement summit that she had organized. He said that he was being denied the authority and the resources to do his job properly.
I remember watching the press conference for his resignation. Quan was staring daggers at him while he stood at the podium. She was NOT pleased.
I know that many people were upset by that. Obviously I can't speak for officers and the way they felt about Mr. Batts, but I can say that lots of regular people were pissed about it. It could be that rank and file officers were also upset and made efforts to undermine Quan.