S.I.N.G is for when you are grabbed from behind bane. You elbow the solar plexus, stamp on the instep then go for the nose and groin. All of which give you opportunity to run. 
I don't want this bullshit about "but they might expect it and your fucked" or "they'll be stronger and you're fucked"

It's just something that could help and they taught it in a film