Possible Clues:

• That's beastly big for Hamlet
• Hamlet might put an end to 23 down
• To a large extent Hamlet was beastly
• Was Hamlet as beastly as that?
• 'Dogged as Hamlet (5,4)'
• One who barks out ''Hamlet'' perhaps
• Angered at wild dog
• Dog that's definitely not a toy
• Dog with a tall body
• Scooby-Doo, e.g.