What type of stretching and specific stretches is he doing? If he stretches correctly it will absolutely help him with pain.
The first thing that he needs to do is figure out the cause of his back pain, then he can start to actually address that cause. Since we have nothing more to go on than "his back hurts", there is really no way that any of us could hope to give you any kinds of educated guesses as to why he is having back pain and therefore can't really give you any ways to fix said back pain.
For instance, his back pain could be the result of:
-getting repeatedly tackled and twisted or slammed into the ground while playing football (you didn't mention what position he plays) and thus he may be bruised or even have injured
-poor form while lifting and thus using incorrect muscle groups and movement patterns
-tight hip flexors and lower back muscles (Anterior Pelvic Tilt/Lordosis/Lower Crossed Syndrome), thus placing his lumbar spine under excessive tension throughout his day and becoming aggravated from his additional lifting/sporting activities
-uneven leg length, thus tilting his pelvis laterally and placing his spine in a scoliotic curve (sideways curve)
-inactive hip extensors (Glutes primarily), thus causing him to attempt to lift things with his back
-weak legs, thus again causing him to compensated by lifting with his back
-tight hamstrings, thus preventing him from maintaining a neutral pelvis while squatting/hip hinging
In short, without details we'd just be throwing crap at the wall and hoping that it sticks.