I have conflicting feelings over this. I know that open carry is a thing in Texas, but who crossed the line, if anyone?

From what you've written, overall the police were in violation but the injuries could have been avoided had the citizens complied with the initial order by the police to get on the ground. This is the kind of incident I expected when Texas passed this open carry law. I don't agree with it anyway but it's the law and the police should pay attention to it if it it's in place. My opinion, this isn't the wild west anymore and we don't need everyone walking around with a gun on their hip.

I really don't know a whole lot about this situation. Indeed, my reading of this post was really the first I'd heard anything about it. I must say though, that Bexar County may have different laws which they may feel apply within the Texas Constitution. I'm certain there's some major legal aspects here which will have to be addressed. Ultimately the Second Amendment supersedes everything. But some people feel that the second amendment has a different meaning in that only National Guard units should be allowed to carry weapons. Others may take a different approach that only certain Firearms are allowed to the citizens of the United States. Others have a much more open definition in that American citizen should be allowed to carry any weapon they choose.
This case will probably go all the way to the Supreme Court. Just where does civil Authority begin and end when it comes to the 2nd Amendment?

I am always somewhat suspicious of stories written in such a manner as to arouse strong emotions in people. It has been happening a lot over the last four years or so. This event in Texas of course is not as serious as some incidents which have provoked city-wide violent outrage over alleged police misconduct.
I was not present in Olmos Park so any information I have been presented could easily have been manipulated. As a former police investigator I have many more questions than answers.
Please note the following from 1/SGT Grisham's Open Carry Texas website:

"CAN I BE ARRESTED FOR OPEN CARRY? You can be arrested for any reason or no reason in Texas."

I do not know why the initial detention occurred (NOTE: detention and arrest are usually different in most jurisdictions). No individual can righteously second guess a LEO who is "honestly" discharging his duty. A police review board or a court may second guess the officer(s) actions but still often make errors. I suspect that the "peace" was disturbed or violated and when 1/SGT Grisham refused to follow a lawful order, was tazed and arrested. Disturbing the peace is a criminal offense though not normally a serious one. A criminal offense of any kind (while armed) in every jurisdiction of which I am aware, immediately invalidates the right to carry a firearm.
As an objective observer I suspect that 1/SGT Grisham was intentionally engaging in behavior likely to provoke a specific enforcement action by Chief Valenciano and/or his department. The use of a taser on an armed individual failing to follow a lawful order is reasonable (NOTE: the law normally sides with enforcement when the officer's or public safety could be at risk). Did the chief over react? I suspect that better communication would have been beneficial for all. Now the courts will decide. Not Monday morning quarterbacks like us.

It's also funny that NO ONE (at least no one whose response I've read so far) has commented that military bases do not allow open carry of firearms unless the person is authorized to do so. Try carrying a rifle onto a military base, or walking around carrying a rifle outside of areas that one expects to find people carrying rifles. Sure, MPs are authorized to carry firearms, and there may be other personnel who are authorized to carry firearms, but there is a reason that firearms are fairly tightly controlled on military bases. Try walking in and out of the barracks carrying a civilian rifle, lounging around in civilian clothes while holding a firearm, and see how quickly the MPs or security detail responds.

Valenciano was out of line! That's one of the things I most admire abou Texas! To have this law abiding citizen get taxed and arrested is unconscionable! Throw theChief in his own jail!

While I respect and support Law Enforcement Officers in general, I also recognize that there are some who 1) don't know the law, 2) don't care, and 3) don't respect individual rights. Those officers must be prosecuted, to teach the others that individual rights trump their prejudices.

Sue the living crap out of them. All they understand is money. When this poor excuse for a " lawman" is broke and his Dept. closed for lack of funds, only then will this type of criminal activity, by those sworn to uphold the law, stop. Hit them in the wallet!

Sue them! All they understand is money. When the Sheriff cannot operate his Gestapo for lack of money only then will police overreaching end. Sue them for all of us!

One of the issues I see is that police officers think they "are" the law, it makes them feel more powerful. But, they are not the law, only the people the "enforce laws" that are on the books. This chief and the officers involved should be reminded of that, and be fired.

Sack the police chief!