The web stores have lacrosse helmet sizes from xxxsmall to xxxlarge. How do I go about measuring what size he needs?
Bring his head with you to a local sporting goods store. OK, fine, bring the whole kid. But it’s something that really does need to be fitted right. If it’s too loose, it bounces around and doesn’t protect the way it’s supposed to; if it’s too tight, it’s just plain uncomfortable and distracting.
Do any of his friend or teammates have helmets that you could check the fit on? Failing that, could you order more than one and then return the one(s) that don’t fit?