if your are experience back pain while playing sports it is most likely your hamstrings and glutes causing the pain if it is in your lower back. if those two muscles are tight they will cause lower back pain, which i have experienced in the past. i have seen physiotherapists and chiropractors and they both had the same comment on back pain.
they both had the same take on how to make your back stronger, they advised to go swimming as it does not have wear and tear on your body but does add resistance.
for before your game stretches they should not be static stretches( stretches where your hold the stretch for a set time) they should be dynamic stretches which involve movement like jogging, arm circles, weightless good mornings, leg swings, bodyweight squats and lunges, etc.
performing static stretches before a game is one thing that should not be done because it will not help you at all and can increase your chances of injury
there is a site full of articles on training, not really in-depth but perfect for a person who is looking to get the jysk of it.