Possible Clues:

• Club not often seen
• Seldom-used golf club
• Its face is almost vertical
• Club used on a 51 Across, maybe
• Club with very little loft
• Driving club
• Designated driver?
• It's nicknamed a 'butter knife'
• Club 'even God can't hit,' according to Lee Trevino
• Club that 'even God can't hit,' according to Lee Trevino