How to become a referee in the US

[italian_referee]

Thank you all guys for all your useful responses!

I have another question: Is it possible to referee games for free voluntarily and have some kind of proof of that?

I am asking this because I am coming to the US with a F-1 student visa which does not allow off-campus employment unless related to the course of studies (in my case it is not related at all), and non-paid refereeing activity may not be considered as employment, and hence I may have some chance of doing that.

Do you have any experience to share?

Thank you all!