Believe it or not, the hamstring is probably the muscle that gets the least amount of attention, in terms of stretching, in jiu-jitsu. There are guys out there that may be flexible enough to put their foot behind their hand but are also unable to touch their toes. In a lot of ways, there are not many positions in jiu-jitsu that naturally stretch the hamstring in this way. Jiu-jitsu can naturally give us flexibility in many positions, but this one that just doesn't happen on it's own.
This is where long time friend of the Jits Magazine, Andreo Spina comes in. In the video below he explains how to properly stretch the muscle without doing very much damage to nerves, because there is a wrong and write way to do it.