There are many factors that go into hamstring injuries. What a lot of people do not know is the glutes play a major role in those injuries. Those muscles must act as a key factor in preventing strains. If the glutes are tight, you are more prone to pulling or even tearing your hamstring.
Another major factor is running form. The body has to be well balanced when you run. When athletes do not have that balance, other areas of the body overcompensate and that leads to injuries. For example, if I am running and I put more pressure on my right leg than my left leg, I am putting myself in danger of injuring my right leg.
Most of this is all science and biomechanics working together, and when one piece is off, everything else has a higher chance of breaking down. That is why strength, flexibility, and technique must all be trained consistently to keep the body performing at its highest level.