Allow me (I am a cop)...
1. Tasers: the max range of a taser is usually less than 21 feet. Tasers that are used by LEOs fire two small barbs into the target, and those barbs are attached by a thin wire. Electricity courses through that wire and into the target, thus causing incapacitation...in theory.
In reality, if a cop misses with one of the barbs, the taser does nothing to the target...at which point the cop gets stabbed/cut/killed. If the barbs do not have enough of a spread between them, the taser will not incapacitate the target, only infuriate, and the cop gets stabbed/cut/killed. If one of the wires break as the target falls to the ground, the taser stops working and the target is able to immediately jump back up, and the cop gets stabbed/cut/killed. Hollywood movies make people think that being tased = being knocked unconscious. That is pure BS.
Tasers combined with mace is a no-no. While the mace itself is not flammable, the propellant can be. If one cop is trying to mace and another is trying to use a taser, you can actually set the target on fire. That is why cops are taught to yell "TASER!!!"
Some people are just insane (drug induced or otherwise) and non-lethal options such as a taser or mace have zero affect on them. Some subjects have yanked the taser barbs out of their skin while the electricity was flowing...now what?
2. There is a "reactionary gap" that cops are taught. If someone is 21 feet away from you and they charge you, you have less than 2 seconds to react before they are on top of you. We do this in training with rubber knives and simunition rounds. Most trainees are taken by surprise when they are "stabbed" by an attacker who started less than 21 feet away, before they could react. This is in a "I know it is coming" scenario. On the streets, it is far different as you never know what is going to happen. Panic and/or disbelief can make you forget everything you were taught.
3. US cops wear body armor that is designed to stop bullets. The same vests do not stop knives. UK cops wear body armor that is designed to stop knives.
4. If you don't want to get shot by the cops, don't do stupid (insert explicative).