hahaha same story here! ddnt wrkout cuz of schhool cert, and now that its over, i went to ninjitsu training and did like bout 50 crunches (diff then the regular ones, a bit more "explosive") and i did only 50....2 days later im still sore....normally inseason i could go for about 250 crunches, (not at once, but in the same hour) and i woulnt be sore the next day......
thing is, you start to lose muscle mass if you stop lifting for months....and yes, you might not notice at first, when u start lifting again, but you will. thats because alot of "lifting" is pshylogical, you think you can do it because you have done it....you lose tremendous ammounts of strength and mass in about 6 mnths.....BUT you do have an advantage over a newbie
you dont have to go through the months of light training to strenghten ur joints and ligaments....probably a week will do, just to warm your body up....and yes, your gains will be faster then before, but you need to shock your body back into growth...i would suggest a week of light training and then explosive training once a week along with ur regular wrkouts....this would help you gain back the mass....and this would help in football if im not mistaken
by explosive training i mean powerlifting AND body weight excersizes like the explosive push ups, (when you do a push up but at the top most movement you proepll your self into the air and high as you can...)
to answer your question...about less then a month should be suffecient