This technique is used against a hammer-fist or a bottle attack.
As your attacker strikes, step forward and to the left slightly with your left foot and use a left-handed head block.
Strike your attackers right hip with your left hand and cup round the back of their right ankle with your right hand.
Pull your attackers right foot forward as you push with your left hand. You should also go down on your left knee at this point with their right foot on your right leg.
Keeping your attackers right leg pinned under your right armpit, grab their left ankle with your right hand and strike the back of their knee with your left hand.
Now pin your attackers left foot to the side of your left knee as shown.
Use your right hand to bring your attackers right ankle to your left hand and grab it as shown.
To apply the foot lock you can now simply push down on your attackers left knee.
To continue the move, bring your right knee down next to your left knee and come up onto your left foot. Be sure to keep their left foot pinned.
Now place the edge of your left foot under your attackers chin and push away with your foot.