I was wondering...

[LaxRef]

If you want to do a spring sport--like lacrosse--you should start contacting people right away. You can call the state HS association or the national association for the sport (e.g., USLacrosse) for info on training, or you can even call a local high school athletic department and ask them who they contact to get officials.

Then study the rules, attend training, buy your gear, and you're good to go.

Depending where you live, you might start out doing youth games or you might do HS varsity games your first year. It's easier to start out doing youth games if you have a choice.