So much leadership lacking it hurts! (4)
I believe the answer is:
ouch
'it hurts' is the definition.
(both might be said when in pain)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for ouch that I've seen before include "Ow!" , "Expression of pain" , "response to a bad pun" , "Pained cry" , "Shout of pain" .)