Rebels in times of trouble, losing head (5)
I believe the answer is:
rises
'rebels' is the definition.
(I know this)
'times of trouble losing head' is the wordplay.
'times of trouble' becomes 'crises' (I've seen this in another clue).
'losing head' means to remove the first letter.
'crises' with its first letter taken off is 'RISES'.
'in' acts as a link.
(Other definitions for rises that I've seen before include "Ascends" , "Moves upward" , "Moves upwards" , "Gets up" , "Comes or goes upward" .)