Plan to block his vigorous blow (6)
I believe the answer is:
mishap
'blow' is the definition.
(I've seen this before)
'plan to block his vigorous' is the wordplay.
I cannot quite understand how this works, but
an anagram of 'his' is 'ish' which is located in the answer.
'plan' could be 'map' (I've seen this before) and 'map' is present in the leftover letters.
This accounts for all the letters.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for mishap that I've seen before include "Unlucky development" , "Unfortunate minor accident" , "An accident, piece of bad luck" , "An accident or unlucky event" , "Stroke of bad luck" .)