If the hit was hard enough to cause an impact on the heart to be the cause of his cardiac arrest I doubt he would have stood up after the hit, IMO. If they were not doing CPR after defibrillation with the AED, then that indicates that the AED reversed the V-fib. If they were still doing CPR after defibrillation, that would indicate that they did not convert the rhythm. Intubation would be an appropriate protocol to maintain adequate oxygenation. After defibrillation it is important to maintain a stable cardiac rhythm, adequate oxygenation, cardiac output, as the blood is evaluated to determine if he had a myocardial infarction. ( heart attack due to a blockage in the coronary arteries). This blockage can occur from blood clots. Most MI's occur due to the narrowing of the arteries due to poor diets, or other causes. However in a young athlete it is very rare. Another cause could be an undetected congenital abnormalitie in the vessels.