Static Stretching Reduces Injury Risk in Runners
It is commonly believed that static stretch (holding a stretch for 30 seconds or more) is believed to improve running performance and decrease the risk of injury. Unfortunately for the proponents of this, there is no evidence to support this belief. Comparatively, an active warm up has been reported to improve running performance, although the injury risk benefit is still unclear. In simple terms mimic the activity you are going to do in order to prepare for it. In the case of running it might also be advisable not just to run but to skip, to side skip, jog and even skip backwards (though take care to know where you are going).
You could also consider performing lunges in different directions and add in 3-4 short sharp efforts slightly faster than your goal running pace in the early stages of the run to get your heart rate up
All these activities stimulate the muscles of the hips, around the knees and very importantly the muscles below the knees that control the ankle movements. Doing these multi-directional movements creates good stress through muscles and connective tissues loading them in different directions that create a resilience and improve their elasticity. These are good things as running is an 'elastic' springy, stretchy activity.
Given the above, this is not to say that stretching is a bad thing. It improves and restores joint range of motion and may help in the arm down period proving relaxation.