Stands for Super Hormonal Overly Aggressive Teenage Guys and is pronounced "show-uht-jee". Basically it is a guy who gets way too into a sport and so can cause bodily harm to himself or others. This is not an endearing term.
Jennifer: I was playing badmitton and this guy hit the birdy at my head so hard it knocked me unconscious!
Stephanie: Wow, what a shoatg!