The back is a very dominant position in jiu-jitsu. Many people have gotten very good at defending the back position, not allowing you to sink in a choke of any kind. The crucifix is a great way to break down their defenses and reward yourself for reaching the dominant position.
1. Go over their shoulder with your foot and push that foot on the ground, effectively trapping one of your opponent’s arms.
2. Slide your opposite foot to the same side as the trapped arm by going under your opponent’s body. They will be bridging and squirming around, so moving your leg into position should be met with little resistance.
3. Once again, use a triangle lock around your opponent’s arm.
4. Work to move your opponent’s defending hand away by pushing it down so you can go for a choke.
You can switch the foot that traps your opponent’s arm for a different way to control.