Mischief-maker joining the Spanish force (5)
I believe the answer is:
impel
'force' is the definition.
(I know that force can be written as impel)
'mischief-maker joining the spanish' is the wordplay.
'mischief maker' becomes 'imp' (I've seen this in other clues).
'joining' says to put letters next to each other.
'the spanish' becomes 'el' ('the' in Spanish).
'imp'+'el'='IMPEL'
(Other definitions for impel that I've seen before include "Cause to move forward" , "Urge forward, drive" , "Send or drive forward" , "'Drive, force (5)'" , "Make" .)