Related Clues:

• Cause of some head-scratching
• Annual basketball tourney
• Izaak Walton's ''very subtil fish''
• Louse to be
• Point to pick
• Detail to pick?
• Minnow relative
• Gripe, gripe, gripe
• Bottom-feeding fish
• Petty objection
• Trivial matter
• Little beef
• Thing to pick
• Bottom feeder
• 21-Across. e.g.