Take the point and dig it into their skin, somewhere soft and sensitive if you can. Behind the knee, on the ankle, or foot, may limit mobility a bit. The best bet is the pain will surprise them long enough for you to break free, or as a distraction to assist a friend.

It's not super practical for defense, however. It will be best used to escape a building or vehicle. Spiderweb the windshield so they can't see, or so a cop pulls them over. Bathroom or back room with a window you can't open? Now you can.