Abdominal pain when exerting himself

My nephew developes severe abdominal pain ( approx. 4 inches on each side of belly button, about 2 inches below and about 5 inches above).  The pain does not go into his sides or back. The pain occurs when he is running and during football practice, he can do things like sit ups with no problems.  He has had a scope in his stomach which we were told was normal, he had a abdominal ultrasound and a MRI.  Originally, after the ultrasound, they said it was a torn abdominal muscle.  The doctor changed his mind and then sent him for a MRI which they said was normal.  The pain is severe but when it's gone, it's gone.  He went to college to play football and now he cannot. If you have any ideas I'd very much appreciate it.  He does not smoke and is on no meds.  (in past he did try something for acid reflux but has since stopped taking it due to the fact that it did not help him)  He is very athletic, football and weight lifting mainly.  He is approx. 6' 0" and weighs about 230#.  

[Cleveland Clinic]

I am not sure what could be causing this appart from a vascular cause, perhaps intestinal angina? Maybe from a malformation from one of the mesentaric vessels? Possibly. This could be assessed initially with either a CTA or n MRA to look for the course of the vessels, to see if there are any 'tight' lesions. Apart from that an abdominal aneurysm should have been excluded via the ultrasound, so I don't see any other dangerous or life threatening causes for his pain.