Your off-season weekly gym program should include two strength training days (superset opposing muscle groups using functional exercises) and a speed/power day (explosive weightlifting movements in a circuit, with plyometrics as intervals), in addition to your athletic skill training/practices on the field.
Do some agility work and sprint starts at the end of your speed/power circuit. Then include 2-to-3 endurance/cardiovascular training sessions each week as well, running for about 30 minutes with short sprint intervals and hill running ... not just long endurance runs.