Split leg pass usually set up via guard pass, starting up you need on knee on opponent’s leg and touching the ground:

1. Snake arm around opponent’s upper leg and get it on your shoulder
2. Apply pressure on that leg by driving fowards
3. keep driving forwards to smash their leg to the ground and step back with your forward leg getting to their back
4. Square up and get side control, if they are facing away from you and you can establish seatbelt, you could do a backtake