One of the best preventions for sports-related injuries is to make sure you have warmed up enough before jumping into intense play or exercise. Stretching the muscles makes them physically warmer as blood flow increases. It wakes the body up, increases circulation, and begins increasing the amount of oxygen flowing through you.
Start with gentle jumping jacks, jumping only high enough to open legs and landing lightly. Start with feet together and open just to shoulder width while raising arms from down at side to straight overhead. Do 10-15 times. Then pick up the pace with crossover jumping jacks. Start with legs apart just a little wider than shoulder width and arms straight out on each side. Jump just enough to move your legs. Bring both legs in and cross over, while doing the same with your arms. Immediately reverse back to starting position.
Start standing straight up, feet shoulder width apart, knees slightly bent. Bend forward from the hips til your torso parallel to the floor, and hold. Stretch your arms down toward the floor, keeping your hands lightly curled as though you were holding dumbbells. Bend at the elbows, bringing your upper arms to shoulder level as your hands stay facing the floor. Your elbows should be bent in an L-shape. Now, holding the rest of your body in place, move only at the elbows to bring your lower arms up. You should finish with your arms even with your shoulders, elbows still bent 90 degrees. Then reverse back to start. Do 10-15 reps.
Start as if you were at the top of a pushup — back straight, hands flat on the floor, shoulder-width apart. Keeping your abs tight, raise your right foot and draw it slowly toward your right shoulder. Hold for 2 seconds, then stretch back out. Do 10-15 on each side.
Lay on your left side with your left leg straight out, right leg drawn up at 90 degree angle, both arms stretched out flat with right palm facing left palm. Keeping both legs and left arm in place, rotate at the waist, bringing right arm up and over until the arm and upper back are flat on the floor. Then bring back to starting position. Do 8-10 reps, then switch sides and do 8-10 more.
Start in downward dog position with feet and palms flat on floor. Bring your right foot forward until it is between your two hands; your left foot will move from flat to flexed with just toes and first part of foot on floor. Next, rotate your torso to the right, bringing your arm up in an arc until it is stretched directly overhead. Reverse back to the starting position. Do 8-10 reps on each side.
This is a good set of overall stretches to begin warming you up and increasing your flexibility, which will help prevent injury as you move into more intense exercise. Follow this up with exercises targeting the most used parts of your body in your sport — legs for running, or a throwing workout for the upper body.