Possible Clues:

• Hatfield, to McCoy
• Last bit of resistance of retreating enemy
• Jay-Z "Friend or ___"
• Goliath, e.g
• Rival fooled in odd places?
• #1 spot, when you're #2
• Paris, to Romeo
• Enemy or competitor
• A personal enemy
• Coetzee's first fictional offering exceptional? He is opposed