An absolute coincidence in my opinion. Anyone who has played football, at any level, will understand that the way you are stretching and extending your legs and the general movement your legs will take during a game means that any footballer will be massively susceptible and vulnerable to a hamstring injury. You can do as many stretches as you like but in the case of a hamstring they can be pulled, strained, torn at any point regardless of any sort of exhaustive stretching or exercise regimes/techniques.