Possible Clues:

• ''Bad call, ump!''
• Deride
• Show disapproval of tedious type right away
• One in an unhappy chorus
• Shout with cupped hands, maybe
• Halloween cry divided in this puzzle's eight longest answers
• Hiss accompanier
• It's said with a thumbs-down
• One-named rock star
• Show disapproval of endless error and reduced volume in short report