For years, people did static stretching before workouts. In fact, you can see many professional athletes doing these kinds of stretches before MLB and NFL games. These are the stretches where you use your body weight to elongate and stretch a muscle without any movement. They're the stretches you probably did in high school or still should do after your exercise.
These are not the kind of stretches that should be done before exercise, though. There are a few studies that have shown that static stretching reduces speed and strength. Pre-exercise stretching should warm up your body and increase the blood flow which increases flexibility in the muscles. Dynamic stretching, as it's called, will help you avoid injury, but not decrease your performance. Static stretching is still a valuable tool, but should be used after your exercise or on different days.
Now there is a new way to stretch before your run or game. You can use a foam roller to stretch out your quadriceps without damaging your strength or performance. The foam roller does increase the range of motion in the knee. Unfortunately, this study only seems to have looked at that muscle group, not hamstrings, and calves.