You're wrong. There is protocol in these situations.
The protocol is using the minimum amount of force necessary. This was clearly over the top. There was need to tase the woman. She was handcuffed. Spin her around, slap her in a cell and charge her with assault.
I sympathize with the cop, and know full well it isn't always easy or even possible to control yourself when you get pissed, but the law is the law, and the protocol was not followed. I don't know that departments policies, but I guarantee tasing someone who for all intents and purposes is under control is a no no.
This situation is actually one of the reasons I didn't become a cop. I really wanted to, but I worried I would lose my s on some dirtbag.