This is a basic technique called de-kote. You strike your opponent’s kote when your opponent is just about to move his/her hands to strike.
Now you MUST know what not to do when you execute de-kote, which I am doing in the video. Now it is important for you to KNOW what not to do and what you should be doing so you can fix your bad habits or at least you can work on what you are supposed to do in training.
Because you see things a lot in shiai videos (i.e. youtube), it does not mean they are correct. That’s why it is very IMPORTANT for us to know what to do and what not to do.