One of the most common things people are told to do when they have the half guard on the bottom is to get an undertook because it will lead to a lot of good attacks. This is very true but sometimes you’ll come across an opponent who has a strong overhook, or just overbooks you in general in an attempt to stop your attacks.
In this video I demonstrate a triangle attack that you can do against your opponent that overbooks you while you have the half guard.
The good thing about this attack is that not many people are going to expect you to actually attack for a triangle choke from this position so you may also have the element of surprise as well.
This is an attack that I like to do often from this scenario.
Hope it helps