Ready to drop tax due? He's crafty (9)
I believe the answer is:
exhausted
'ready to drop' is the definition.
(thesaurus)
'tax due? he's crafty' is the wordplay.
'crafty' indicates anagramming the letters.
'tax'+'due'+'hes'='taxduehes'
'taxduehes' with letters rearranged gives 'EXHAUSTED'.
(Other definitions for exhausted that I've seen before include "Dead-beat" , "ready for bed" , "Complete fatigued" , "Worn out" , "Drained of strength" .)