They are present on stirring occasions (9)
I believe the answer is:
agitators
'stirring occasions' is the definition.
Although both the answer and definition are plural nouns, I cannot understand how they can define each other.
'they are present on' is the wordplay.
I cannot really understand how this works, but
'are' could be 'a' (short for 'are', historical unit of measurement) and 'a' is found in the answer.
'on' could be 'at' (I've seen this in other clues) and 'at' is found within the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for agitators that I've seen before include "Rabble-rousers" , "revolutionaries" , "A gait rots the stirrers" , "We wind up" .)