Dropping somewhat ambitious catch (4)
I believe the answer is:
scat
'dropping' is the definition.
(I've seen this before)
'somewhat ambitious catch' is the wordplay.
'somewhat' indicates a hidden word.
'SCAT' can be found hidden inside 'ambitious catch'.
(Other definitions for scat that I've seen before include "Buzz off" , "Wordless singing style" , "it's dropped by 21 [SNAKES]" , "Type of jazz singing - be off!" , "Leave; jazz singing" .)