In short, leader's intervention in niche activity is the issue (8)
I believe the answer is:
children
'the issue' is the definition.
(I've seen this before)
'in short leader's intervention in niche activity' is the wordplay.
'in short leader's intervention' becomes 'ldr' (I can't justify this - if you can you should believe this answer much more).
'in' means one lot of letters goes inside another.
'activity' indicates an anagram (letters become active).
'niche' anagrammed gives 'chien'.
'ldr' put within 'chien' is 'CHILDREN'.
'is' acts as a link.
Can you help me to learn more?
(Other definitions for children that I've seen before include "Sons and daughters" , "Offspring" , "Minors" , "Kids" , "Little people" .)