try vitamin a, at doses of between 50,000 and 80,000 IU/day. (most drugstore versions of vitamin a are only 8000 IU per softgel, so this is going to amount to about 7-10 softgels per day.) most people are way underdosed on vitamin a, and boosting it to those levels can have drastic effects on energy levels throughout the day.
also, you should have him take a sublingual vitamin b-12 tablet, preferably 5000mcg if your drugstore carries that dosage. don't just use a “b complex” vitamin, as those tend to have basically negligible amounts of b12.
honestly, if you can get vitamin a and vitamin b12 to the right levels, your son may find that those two alone give him better (and longer-lasting) energy than pre-workout supplements.
in regard to the pre-workout supplements: your son should be EXTREMELY aware of the potential for dependency, both psychological and physiological, on those things.
don't forget hydration, either; a lot of people don't drink enough fluids (or don't drink enough water, relative to fluids that are not water -- in general, you should try to drink 2-3 glasses of water for every 1 glass of a drink that is not water.) that may also be making a difference.
especially if these guys are practicing in full pads, the effects of dehydration from practice can last for hours if your son doesn't chug the water like crazy.