Here are a few simple ones:

Football / Basketball:

“Fun-da-men-tals!” *Clap Clap Clap-Clap-Clap* (2x max)
Good for Pre-Snap penalties such as False Start, Encroachment (Offsides), or Delay of Game. In Basketball, it is good for every traveling, double dribble or stepping out of bounds call made.

“You Can’t Do That!”
Let the opposing team hear about it for every penalty they commit. Also works for every foul committed in Basketball

“Start the Bus!”
About to secure that huge win at home? Let the visitors know about it. Keys are great for added effect! Works for both sports!

I know there are plenty more of possible chants out there for HS. I hope this gives you some ideas to work with!