Are questions like this allowed? It seems mentioning video link in a question post is against rules but I never get to read code of conduct until now. I explain everything in my question post and give link in the end to the lecture as these lectures are popular but still I received warning three times by the same user on linking video. Is this a bad practice?
In general, we expect posts to be self contained so that all details needed are provided & users do not have to go off-site to find out what you're really questioning. Hence, you should provide a link for additional reference to the post, but it should not be a requirement to understand what it is you are looking at and/or questioning.
Ben's comment says,
Please don't post videos. Write a summary so we can tell what the argument is without watching a video.
In this case, he's right: you're requiring us to watch a video to understand what is being explained by Prof Lewin that you are questioning--you really don't describe anything in the post itself (i.e., what is $T_1$, $T_2$? What rope? What cylinder?), it's all in the video you link.