Hello there....you are a young Lad and with a good and active lifestyle.... dont worry cramps in the muscle are a very common occourence...what you need to do now is.....Remember IMS. Whr I-Ice,M-massage, S-stretching. Icing is important to reduce swelling and decrease the sensitivity of the nerves for pain.... keep the ice pack wrapped in the towel at the back of your thigh for 15 mins approx repeat it for 4 to 5 times a day. After icing sit on a chair and try and extend your knee ie straightn your affected leg once you are able to do it without pain then bend a bit at the waistline this will add more stretch to your hamstring muscle... keep this position for approx 30sec and repeat 5 times. Once you are done with stretching in the straigh leg position with your both hands squeez the hamstring muscle and release like kneading a dough...this will act as a massaging technique. And on top of all this just remember keep yourself hydrated during any demanding activity/sports Instead of fizzy or energy drinks what u should do is always take electral powder and mix it with water and keep it handy. You will never suffer from cramps again if you follow this advice. Take care Do resort back to me if you have any doubts. Regards.

Try dry needling.. It can work magic for you

U need icing 3 times a day elevating leg on pillows and rest which together will reduce the inflamation and pain.u can go for taping ur muscle to relax it.it will support you in walking as well.go to a therapist for taping and use icing as a home remedy.

Take a break from strenuous activities to allow the injury to heal.Use a cane or crutches to avoiding putting your full weight on your injured leg.Apply ice packs several times a day to relieve pain and reduce swelling.Wrap the injured area with a compression bandage or wear compression shorts to minimize swelling.Rest with your leg elevated above the level of your heart, if possible, to improve drainage and minimize swelling.Take an over-the-counter pain medication,such as ibuprofen. If your muscle has pulled free from where it's connected to your pelvis or shinbone, orthopedic surgeons can reattach it. Severe muscle tears also can be repaired...