Related Clues:

• U2 singer
• Pro ___ (like some legal work)
• See 59-Down
• -- -tat-tat
• Rock singer in social causes
• With 59-Across, a knock
• 'With or Without You' lyricist
• U2's lead singer
• U2 vocalist
• For free
• Activist singer from Dublin
• 'With or Without You' singer
• "The Beat Goes On" singer
• Pro ___ (free)
• Pro --