Possible Clues:

• Lean part of the anatomy
• Not the sole support of a rotter in 27 across
• One of the crusty ends of a loaf 
• Achilles’ soft spot
• Bounder; part of foot
• Darned spot, often
• Foot back
• He's bad and not one's sole support
• Lean fellow not to be trusted
• Hot fish provided in part of golf club