Hi Grant
As I don’t know what you did at the game before you developed the pain, it is a bit hard to know what is involved. A number of structures can refer pain to the area you describe including the lower back joints ,sacroiliac joint, hip joint and a number of associated muscles can also refer pain there.
If you think the injury may have been from a stretch to the hamstring a very common underlying problem is not the hamstring muscle but rather the sciatic nerve. The dura – the tissue around the nerve or the nerve itself may have got stretched. When you bend the hip while straightening the knee you not only stretch the hamstrings but also the sciatic nerve. sitting, driving or over extending my hamstring whilst sprinting are absolutely typical positions and movements which can aggravate an injured sciatic nerve or its dural sheath and the dura typically refers pain to the buttock and down the back of the thigh as if it is an injured hamstring.
A physio with a sports of musculoskeletal speciality can examine you and sort out what is really going on. If I am right (which I may not be) about the nerve problem the physio can mobilise the nerve and advise you on rehabbing your leg. In the mean time don’t do any stretching to it.
Geoff