Possible Clues:

• One perhaps who might be boxing in the source of 20 down
• That's hole in the top of the tracer
• There''s a hole in the top for a boxer, perhaps
• Hole of volcano or bomb
• One might perhaps get you a box or get you a hole on top
• Hole left by explosion
• Perhaps it's the boxer that's the whole of the top, by the sound of it
• Capital of Virginia
• Impact hole
• Fail suddenly and spectacularly