If you have not seen this situation from earlier in the year, check out the semi-complete video released recently.
It took me a bit to find the reason for this whole thing, apparently, in Chicago, it is against city ordinance to move from train car to train car while the train is moving. Is that a good reason to make contact with someone, as a LEO? Yes. You are allowed to do so as it is in direct violation of a local ordinance that exists for the purpose of keeping people safe. It's also textbook "reasonable suspicion" as a person is doing something which is, in and of itself, may not be immediately criminal but warrants a LEO to investigate a little bit further. However, once a LEO decides to make contact with a citizen, there are two fundamental concepts that need to flushed out immediately.
When any law enforcement officer decides to make a stop of a person, regardless of how that person feels about that stop, that LEO has to understand that they should be willing to take every reasonable measure to detain that person. The word reasonable is very important here because it is wholly unreasonable to use deadly force. However, the act of resisting an arrest and/or assault on a law enforcement officer may escalate the obvious need to use deadly force. The citizen who is being stopped by the police may take direct action against an officer who is stopping them, and because of that direct action may facilitate a deadly force confrontation. There were several of these types of situations which recently occurred, this situation in Chicago does not reach that level in my opinion, but others have. If you notice here, in this situation the citizen had the ability to take the officers taser and use it against them, he did not. He could have attempted to disarm one of the officers, he did not attempt to do so. He did not pose an immediate or deadly force threat to others as he was attempting to escape up the escalator, yet he was still shot.
LEO's need to make the right choices when they decide to make these citizen contacts. When I teach new officers how and why to stop someone for something, the first thing I always tell them is "are you willing to kill this person if they decide they aren't going to comply?" The answer is almost always "hell no" which is the right answer, especially in this particular situation. In fact, the vast majority of police stops of citizens will not result in any force at all, so when there is force there may have been a breakdown in the understanding of the concepts which guide the LEO's who made that particular stop.
For example, if this guy in the video decided to run, which he did, and the officers simply shrugged their shoulders and let him go, what exactly would have been the issue? They let a guy go who was, at best, committing a citeable offense with a max fine of a few hundred dollars. The threshold of violence needed to enforce these types of offenses should always be extremely low, only inexperienced LEOs would try to turn this into a big deal. Flip that around, if the guy they were trying to stop completely matched a description to a robbery by firearm, where he pointed a gun at another person, which had just occurred and when the officers approached him he ran, would the same officers be justified in trying to stop him using some kind of force (below deadly force, until presented with such a threat), the short answer would be yes. This is because if this person got away they may try to rob someone with a firearm again, they may shoot someone or worse yet another officer who unknowingly was in his path. Remember the bad guys know what they did, the LEOs don't at the initial onset of contact.
This all, however, is a double-edged sword.
As a citizen of this country, a country of laws, you have a fundamental responsibility to yourself, and your community, not to cause a disturbance and suck resources away from other citizens who may need them more than you, especially if you don't actually need them. Being stopped by the police may be a temporary inconvenience in your day, and this ramps up drastically when you do not comply with the officers who stop you.
Consider for a moment that the citizen in the subway in Chicago simply complied with the officers, provided his ID, and got his fine for switching cars. Would he have been shot? Beaten? Would he have the opportunity to sue the city? Would he have to go through everything he did? Likely not, although many anti-police people would have you believe this is a normal occurrence in the world of LE. This is simply false (other than people suing departments constantly), and to level an accusation against all LEOs because of a few really inexperienced, underqualified officers who lack basic skill sets that are required for a competent and reasonable officer is extremely short-sighted. The sword does indeed cut both ways here.
But then how do you fight injustice? Easy! In court, through the complaint process, through the media. If a LEO did something to you which you believe is so egregious that causes you to seek a lawyer to sue their department, should also cause you to make a formal complaint against that officer for their conduct and should also make you reach out to the local media outlets to cover your story. Fundamentally, the best way of changing a police department's policies is to fight them in the legal courtroom and in the court of public opinion. Remember the top brass are weaklings, they will fold and bend the knee to public opinion extremely quickly. Remember, none of the above-mentioned actions of recourse relieve the citizen of their responsibilities during a police-citizen interaction.
Beyond all of what is said above, a LEO should have a basic understanding of interpersonal physical violence and should be able to use those skillsets to stop any physical situation from escalating to deadly force, especially when the escalation stemmed from that LEO's inability to physically control that non-compliant person. Now understand there is a clear difference between a person who is trying to escape arrest and someone who attempting to assault a LEO, those two situations may appear similar to the untrained eye but they are in fact different in nature. A LEO should go out of their way to learn basic BJJ, American boxing, Thai boxing, wrestling, and a myriad of other martial arts concepts. They do not have to be a master in any one of those specific martial arts in order to perform well, but having a well-rounded understanding of how you use force without resorting to deadly force is a fundamental aspect of police work. A LEO should never expect his department or agency to provide such training, they won't, it always falls to that individual LEO to learn how to do these things.