Remember your gritty, old P.E. teacher with a head like a can of baked beans and a body like a public mailbox? He was horrible, his knuckles white with rage, his life painfully unexamined.
In my P.E. class before my classmates and I were allowed to mindlessly pelt each other with red balls, we had to stretch. We were told that we needed to stretch in order to protect ourselves from soreness and injury.
Your P.E. teacher was wrong about the choices that he made in his life, and he was wrong about stretching. Numerous studies have found that stretching does nothing. It's the bric-a-brac of doing things.
Some say that stretching may even be harmful, because it makes your muscles all pliant and more vulnerable to injury.
Others claim that some light exercise before the main event may help get circulation going, but that it's more like exercise foreplay and doesn't have a whole lot of therapeutic value.
According to experts, (even those who still claim that stretching is key) the best way to avoid exercise injury is to stay active and listen to your body. If you leg hurts, maybe you should rest it.
Talk to a Sports Medicine Physician about the risks of exercise injury.
Find a local doctor.