Every story has two sides and things on the other side - police officers bitten to bleed or eyes flashed by high power laser pointers. The sad thing is, we gotta take whatever the media feeds us:)
We could talk about reasons and sides, but that's misleading and unproductive. The sad reality is that China is a "Unitary one-party socialist republic", a bad euphemism for an undemocratic country ruled by a single dictatorial party.
There's a lot of misinformation surrounding the violence of protesters, but let's not forget that these officers are protecting the interests of a regime.