In reference to my recent post on stretching, I'd like to add that muscle functionality is more important than overall strength in injury prevention. Stretching, does not train a muscle within it's functional capacity in relation to movement; both linear and transverse.

Conditioning Research and Vern Gambetta have a great post on this.

Another reason is too much emphasis on linear running mechanics, very little on turns. The hamstring is a transverse plane muscle that is stressed when running a curve and on deceleration. There is too much strengthening using non functional exercises in prone and supine positions.

Vern's solution is simple;

More lunges in all planes, step-ups both low and high, more emphasis on running turns and at least two days a week of all out sprinting outside the game. It takes time and preparation with attention to detail.

He's talking baseball, but the theory is most important. All muscles should be trained functionally to prevent injuries and keep you training hard, playing harder, and staying healthy.