Some other cases are:
1. Police ground a protester's face on the ground, breaking his teeth and injuring his face:
2. Police shot "bean bag bullets" at a protester's eye, rupturing her right eye and caused permanent blindness:
3. Police fired tear gas and rubber bullets into MTR (subway) station at normal operating hours:
4. Police disguised as protesters to incite to riot and capture real protesters:
(Same link as (1))
5. While they were insistent and brutal in arresting protesters, HK police assisted and protected triads AGAIN as they attack civilians:
Someone already lost an eye few months ago.
President guard is disguised as a policeman and beat some people on the streets. 
And on and on. The issue is that people are starting to lose trust in how the police and the gouvernment operate and are seeing that some actions don't seem fair to them.
 : https://www.youtube.com/watch?v=eDom3fi67ew
 : https://www.youtube.com/watch?v=IMXeosboyjg
 : https://en.wikipedia.org/wiki/Benalla_affair
I still remember French setting fire to dozens of cars in several different protests, while the police was too afraid to intervene, or be accused of curtailing those "peaceful" citizens rights to express themselves as they see fit.
Well, not that much, the protests in question could probably be far more peaceful if the CRS had a a lighter hand on the tear gas grenades, the flash ball guns, the sticks and everything.
Just to illustrate, the last year protests saw the reappearance of the "Voltigeurs" (cops on motorcycles with sticks and flash ball guns), these units were disbanded in the 80ies after the death of a student.
And the casualties list is pretty significant, 2 deaths, several hundreds injured (including a few lost eyes and hands).
Are these protests borderline riots? yes. But the Police response is also quite bad. I'm personally wondering if it's a conscientious political decision to have an heavy hand to breed violence in order to then 1) discourage other people from protesting 2) discredit a movement.
Granted, France is not yet at the level of China, we don't see opponents to Macron being jailed or disappearing (even if some developments are quite worrisome).
The State has a legitimacy for violence through its police and military forces that individual citizen don't have, and that's a good thing. But it also mean that the State must be extremely cautious about its use of violence to keep a moral high ground, specially in the context of a Democracy.
Lastly, History is generally not very kind on violent repression of protests and riots, even when at the time, the vast majority agreed with said repression.
And what's wrong with firing tear gas and rubber bullets during "normal operating hours"? There was probably no legitimate non-protesting traveller in the Kwai Fong MTR station anymore. I don't think you can ever be 100% sure that there are no innocent by-standers in the crowd. So what is the police supposed to do? Never use force against protesters?
"Did you throw it?"
"No! Tilly did!"
"Did you bump her when she was swinging?"
"Did you touch her at all?"
"No!" (he's holding a tiny 80s troll figurine in his hand)
"Did the troll toy touch her while you were holding it?"
This reminds me of mobile robots I do cartography and "city planning" for. You can draw all kinds of complicated road networks of one-ways and no-gos and speed limits but the robot will still find that little sliver between two polys and barrel down it at full speed going the wrong way.
Compressed gas pepperball markers is also something used in riot control. I'm not very familiar with guns and all, but I wouldn't be surprised that
1) the two have different intended uses and different intended ranges;
2) one hurts more than the other (though I don't know which one).
factfindingisfn's statement is either factually correct or factually wrong. But I saw him downvoted with no explanation. As of this writing, the other comment in this thread doesn't seem to address the factual claim at all.
Protests (again, in western democratic countries) can be peaceful, and typically are peaceful provided the police don't escalate things.
"Natural reaction" it may well be, but they're meant to be a professional police force; not a street gang.