It's hard to reverse, perhaps, without starting! (6)
I believe the answer is:
severe
'it's hard to' is the definition.
(I've seen this before)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for severe that I've seen before include "Harsh, rigorous" , "Serious or strict" , "'Strict, harsh (6)'" , "Harsh and stringent" , "Acute" .)