Plant a resistance fighter in the outskirts of Hull (8)
I believe the answer is:
harebell
'plant' is the definition.
(harebell is a kind of plant)
'a resistance fighter in the outskirts of hull' is the wordplay.
'resistance fighter' becomes 'rebel' (I've seen this before).
'in the' indicates putting letters inside.
'outskirts of' says to hollow out the word (remove centre letters).
'hull' with its middle taken out is 'hl'.
'a'+'rebel'='arebel'
'arebel' going into 'hl' is 'HAREBELL'.
(Other definitions for harebell that I've seen before include "Pale blue flower in beer hall, oddly" , "Wild hyacinth" , "Plant" , "Delicate blue campanula" , "Blue wild flower -- beer hall (anag)" .)