Related Clues:

• Second opening?
• The "A" of ABM
• Knock or social preceder
• Nay voter
• Prefix for freeze
• Second starter?
• One who's against
• Definitely not a pro
• Social starter?
• Side in an argument
• One who hasn't turned pro?
• Prefix with knock
• Planning to vote no
• Knock or social attachment
• Debater's position, perhaps