if you're going to be doing cardio, do it first thing in the morning. i have noticed a huge difference in cardio effectiveness by doing it as soon as i wake up.
add a high quality flax seed oil to your diet, say 1tsp a day. one of the benefits is that will help prevent the breakdown of muscle tissue. if you're not against supplementation, a good glutamine supplement is an excellent anti-catabolic that you can take in place of the flax seed oil. you'll need those things b/c if you should decide to drop you calorie intake and continue to play ball, life, and do cardio, your body might start to breakdown muscle for energy. however, i would NOT drop calorie intake that much especially if you're a football player...you're going to need them for knocking people on their ***...unless you're a kicker
skew your diet so you're getting about 40-50% of your calories through protiein (chicken/turkey breast, tuna, etc.) eat vegetables instead of fruits. cut your sugar intake and eat smaller meals more frequently throughout the day. what naxis said about water and sodium is spot on. fat and water retention are the big obstacles....luck!