Ok, while that is generally GOOD information, it is not always wrong to grab from behind. Sometimes, it's your only choice.
For example, my FLWC veiled is impossible to handle most of the time unless I am restraining him. The application of ANY pressure on chameleons makes them very very afraid and angry.
When dealing with a chameleon that will bite you if you do not restrain them, you just have to choose: Bloody, nasty wound(s) on my hand, or a stressed and pissed off chameleon.
That chameleon in the bottom video, while "unfriendly" is not extremely aggressive, as chameleons go!
I will not handle a really mean chameleon unless it's a medical problem. It is easy to extricate (for transferring them, usually with the aid of a stick)even the nastiest ones without grabbing - but if you need to look at them, or preform some medical procedure, you have to grab them.
My FLWC had a ton of unshed skin around his feet, squeezing his toes and messing up his feet in general. I had to hold him while I yanked the skin off his foot - multiple layers, all over his feet(including the bottoms), had to come off. I had to apply mineral oil, and then mess with him later to get it off. He hates me for it, and it will take time for him to hate me less. But it had to be done.
I have found that with super-nasty veileds, sometimes, they react poorly IN their cage, but not so badly once out of it. A grab from behind - gently - nutralizes their jaws. Once out of the cage, you can handle them normally, without fear of beign bitten.