No football experience but my son plays hockey...
My son was playing hockey on a competitive and his school teams as well as being in two phys.ed classes per day (one of which included weight lifting) when he became sick. During the months in searching for a diagnosis, he lost 20-25 lbs, was fatigued, anemic, etc. and this all took a toll - he continued playing/participating as often as possible but you could easily see he was struggling. By the time we got a diagnosis in May 2011, his regular hockey season had ended but he had moved onto summer ice hockey and ball hockey... So I had a chance to see his sports performance before, during and after diagnosis and treatment...
Once he began treatment (EEN), he responded very quickly and was back at his phys.ed. classes a couple of weeks later (albeit at a slower pace), he added back one hockey team and then the other within a month. He did have to take breaks sometimes and just generally take it a bit slower. By the end of summer though, crohns wasn't really having a direct impact on his sports, however, it probably took until approx. November before everything was back to 'normal' - weight, strength and endurance. The only thing that bothered him was long distance running - a 5 km run was part of the phys.ed. program and training for the run caused him pain every time. However, short/quick distances, such as the running in ball hockey, did not have this effect.
The winter hockey season following his diagnosis was actually the best he'd ever had! And he's continued to play hockey since (almost 3 years). He's also continued with weight lifting sporadically.
Throughout this time, he was on supplemental EN, taking in 1500 cal per day, 5 times per week - I very much believe that the nutrition he gained from the EN helped his body recover and helped build his weight and strength. I would really encourage some supplemental nutrition as any sports activity will put extra demands on the body and maintaining a solid nutritional status is already a bit of a challenge with crohns.
I know for my son, if we had told him we weren't going to let him play, that would have been more heartbreaking then the crohns diagnosis! We were worried that he wouldn't take breaks when necessary, that he'd push himself too hard, that he'd get frustrated or hurt... but, decided to let him try and see how it went and it hasn't been a problem. We did very much stress to him that he was the only one who could determine when he needed a break and he had to show the responsibility to take one when necessary (and he did.
). But, we also spoke with his phys.ed. teachers and coaches and all were very supportive.
Our GI was also supportive and said his goal was to get him living the life he lived before diagnosis...
As far as injuries - since then, he's had a knee injury, separated one shoulder and dislocated the other :yfaint:; all healed well, had no impact on his crohns and he recovered as well as he would have without crohns/treatments.