Magic works in funny ways, and of course their selection of tools were all magical to some degree. Prepackaged stuff has safe, predictable results when used correctly, but this had been anything but. They'd quite thoroughly bound themselves up in the various and now somewhat broken spells, and the effect was a powerful one.
Mike was now huge, far more so than the simple spells should have allowed, and the jock strap barely contained him. It had to come from somewhere, and it was.
The crowd of jocks watched Simon in awe, who himself was in too much shock to react much. Most of them began rubbing their jock-covered crotches, painfully aroused by the sight. After a moment, they all started looking around, red faced, trying to cover up what they'd just been doing. They were all straight! Except... their insistant boners weren't going away.
Normally, none of them would let something like this pass without mocking the guy with the hard on mercilessly, but since it was all of them, noone was willing to speak up. But shouts broke out all around when they started realizing they were changing!
All around the former skinny kid, muscles were melting away. Body hair, sparse or thick, all disappeared. They watched in horror as shoulders narrowed and limbs grew slender and shorter, the rugged looks of post-pubescent faces rounding into soft, often cute boyish faces.
Mark, the captain, took the worst of it, shrinking down to barely 5 feet tall. The only sign that he wasn't a grade schooler was the 4" erection, the only thing still holding up the nasty jockstrap he wore.
The transformed Simon took this in, giving Mark a predatory look. The former athelete startled, and the jockstrap tumbled to the floor. Mark laughed deeply at the pathetic little toy jutting from the ex-captain's crotch.
He surveyed the room, taking in the crowd of boys, formerly men. Short and skinny, sometimes lanky, but always small and weak, Simon could feel his total domination over them all. His monstrous 10" cock rose and throbbed at the knowledge, and it had a strong effect on everyone around him, as a dozen or so horny, helpless teen boys had little choice but to push their useless jockstraps off their insistant hardons and begin masturbating to their new master's power.