I have a strong belief that yoga should never injure the body it should do the exact opposite, heal it. If you for some reason overstretched your hamstrings or got a tear it is important to work correctly to heal it faster. First you need to be very careful with stretching and instead build up stability and create blood flow in the muscles. The more blood that flows through it the faster it will heal, that is why it takes such a long time to heal an injury when it in the attachment of the muscle.
Take care of your body and hopefully with this class your body will heal faster.