Stuff coaches say

[Rich]

Summer?

I'd probably just smile and walk away.

I'll get a chance Sunday. I'm working games 3-6 of my summer. Disney money.

[Kansas Ref]

Good on the spot decision to "kill the play".
No one is out there being paid to be at the gym but you. It is your responsibility to monitor such activity. In this day and age when everything is videotaped [and your game may have been being recorded on a cell phone as mine usually are by fans instands], then as an Independent Contractor (read as: hoops ref) they [the injured kid's parents] could hold you liable if that injured kid started convulsing and you just let a game continue on without giving a chance for medical or helpful assistance.