For those bodyweight trainers that are not familiar with the bootstrapper squat,here is a great explanation given by Scrapper of "http://www.trainforstrength.com/".
Pic. 1 The starting position is usually the most difficult for people to visualize. They either have their hands too close to their feet (or fingers under their toes!), too far away to maintain balance or their arms are inside their legs creating potential elbow damage. The starting position is crucial to performing Boot-Strappers correctly, so learn to set yourself up right the first time and keep it up every time!
Start by squatting down and balancing yourself, momentarily, on your toes and get into position by slowly leaning forward and putting your hands on the ground just forward of your shoulders. Make sure to keep the toes pointed forward with heels off the ground, and that your knees are together. Relax your body and maintain a 60-40% weight distribution between your feet and your hands with your Hamstrings and Glutes resting on your heels. (pic. 1)
From the starting position all you have to do is try to straighten your legs and stop when your heels touch the ground. From there bring your Glutes back down until they touch your heels and you've completed 1 repetition (or half a repetition if you're doing these in 4-count fashion). (pic. 2)
Quick note: If you feel this exercise in your hamstrings, you are suffering from poor flexibility. Bootstrappers will burn your quads like few other things will! Mixed with various other exercises Bootstrappers quickly point out the weakest link in your body.