The S.I.N.G tactic is handy for fighting back against a rapist who attacks from behind.
S - solar plexus (breast bone)
I - instep (inside the ankle)
N - nose
G - groin
Elbow the rapist in the chest (solar plexus) Stamp your foot hard on the inside of his ankle. Elbow the rapist in the nose/face. Elbow the rapist in the groin.