How do I use underhooks effectively in BJJ?

The underhook is achieved by threading your arm under your opponent armpit and controlling their shoulder or back. This inside position gives you leverage and control over their movement. In half guard bottom, getting the underhook is priority one because it lets you come up to a dog fight position for sweeps and back takes. Without the underhook, you are usually on the defensive. In standing grappling, the underhook enables single legs, lat drops, and body lock takedowns. In side control bottom, fighting for the underhook creates space for escapes and wrestling up. The battle for underhooks is constant in BJJ. When you have it, you advance. When your opponent has it, they advance. Develop the habit of always fighting for the underhook and pummeling to regain it when lost. In no-gi especially, the underhook is the primary grip that determines who controls the exchange.