Ok, so just to clarify, you say it is perfectly acceptable for a police officer to physically assault a member of the public who is excercising their legal right to peacefull (non-violent, as opposed to silent) protest with no warning given, and when the assaulted person voices their displeasure (still no physical danger to the officer, even from a freshly sharpened screeching voice) you say he is justified in drawing his batton and again without issuing a warning, strike that non-violent protestor, hard enough to cause physical injury ?
As I always try to convey, try to look at the incident from both sides...
Consider it from the officers side. If it was you, and a highly charged stranger came into you face. You have every right to protect yourself. So you push (or slap) them away, and they come back even more highly charged? Would you use the tools available?
And also consider, yes she had every right to protest in a peaceful, non violent way. Her protest was against capitalisation of G20 - nothing that gives her the right to give a load of verbal to an individual just because its his job to try to maintain law and order.
Unrelated, but what do those protesters hope to achieve? If they want to change politics, they need to be on the inside, and by 'inside' I don't mean the slammer...
Ear Defenders should be standard issue then 
I have to admit that when I see some of these protesters I think "Get a hair-cut, get a job, get a life". A few are there because it's a way of life (I don't mean the majorityof them), but none of the officers involved in assault incidents or their colleagues were in danger or had any need to defend themselves.
Hmmm, human nature to defend yourself. Remember, the police were outnumbered probably 100 to 1, protesters shouting and possibly enciting worse, plus they had probably heard on radio that other parts of protest had turned violent (smashing the shite out of RBS branch)?
If you look at the 2 clips featuring the protester getting a shield in the gob, if you look, the protesters are slowly forcing the police towards a wall. Why do protesters need to do that - their argument isn't with the police, but they turn on the police.
Another clip from same day shows protestors completely surrounding about 30 police. Why? Surely thats intimidation enough to get the police adreniline pumping?
The fact remains, why are protesters giving grief to police?
I do work with an ex-plod who was one of the ones put up in front of the miners in the 80s, and how is that whole saga misreported. The more vocal of the protesters, who are always the ones in your face, are the ones who will cause trouble, and will pull a knife - no wonder the police are on edge.