On the original subject of neck cranks ...
Using and defending against neck cranks is part of the martial art of BJJ. They're not allowed in a lot of competitions for a couple of reasons.
Firstly, if the submission goes wrong, a neck injury is more serious than an equally severe arm injury. But also, there is a greater range between "starting to hurt and I'll feel this later" and "something is definitely getting broken" in neck cranks than, for example, arm bars.
With arm bars, you should know that you're in trouble before the pain sets in and you should definitely be tapping by the time it hurts. (Unless maybe you're a pro athlete fighting for world championship prize money that will pay for your medical bills.) It's pretty clear when you are in danger of getting your arm broken.
On the other hand, a lot of neck cranks, unless applied by an expert, are just uncomfortable and leave you sore afterwards, but aren't sufficient to actually break the neck or induce permanent injury. So the person on the receiving end who isn't able to defend/escape is left with a few options:
- Tap based on discomfort/pain rather than the threat of injury. Part of submission grappling is learning to distinguish between the two and usually submit to the later rather than the former. Tapping just based on pain can give a false positive to the sparring partner, since the technique likely would not have finished the fight in the high-adrenaline context of a street fight or high-stakes competition.
- Not tap, endure the discomfort, but then end up sore for the next week and possibly miss training sessions.
- Not tap, then discover that they misjudged and that the crank actually was strong enough to induce real injury.
For this reason, I discourage cranking on necks during sparring unless the practitioners involved have the experience so they know how to apply technical neck cranks that threaten injury rather than discomfort, how to defend neck cranks, and how to recognize and tap to real threats.
That said ...
A lot of legitimate chokes will end up having a neck crank component if they aren't perfectly applied. Ideally we want to have the cleanest possible chokes so that our partners can tap and not end up sore the other day. But if you get caught in a choke that also has a crank component, just tap and move on. Don't pretend that your partner was somehow cheating because they didn't have the perfect application.
Beginners will grab your head and/or neck and squeeze because they don't know what else to do. A squeeze is not a crank. A neck crank is when your opponent bends or twists your neck beyond its safe range of motion. You need to know how to defend this. (The details of how to do this depend on what sort of crank is being applied.)
There is a lot of legitimate head/neck manipulation that falls short of a neck crank. A powerful cross-face is one example of this. The idea is not to bend or twist the spine to the point of injury, just to compromise the alignment so the opponent becomes structurally weak.
There is a tendency to think of neck cranks as just the application of brute strength by big guys, but there is a lot of technique involved in a proper neck crank.