Roger Gracie is known amongst many things, for his crushing pressure, especially from the mount.
When you reach the mount, one of the most common reactions by an opponent is to cross their arms to defend from the incoming armbar. What often happens is that when you attack one arm, the opponent will switch the grip so as to defend that arm.
It’s important to know that and have a good counter that is ready to go, as Roger Gracie teaches here.
Roger likes to control one arm with this smart grip detail from the beginning, which makes it impossible for the opponent to defend the armbar.
This really works. Check this out: