Tight hamstring muscles are common and most of the time will not cause a problem. However they may be more prone to severe strains or contribute to other problems such as back pain.
In addition to an increased injury risk tight hamstrings may affect sports performance making some techniques difficult or impossible such as in high hurdling or martial arts techniques. Forcing a muscle to move at speed outside of its comfortable range will increase the chance of a muscle tear.
Stretching the hamstring muscles
Even if you are not naturally supple you can still improve your flexibility by stretching. Types of stretching include dynamic, static, passive and PNF. Avoid ballistic stretching which is bouncing and forcing the muscle to go further than is comfortable and will damage it. Sports massage can help in loosening tight muscles. Have a regular sports massage on the legs.