Puzzle supporter rallied trainees (11)
I believe the answer is:
brainteaser
'puzzle' is the definition.
(I've seen this before)
'supporter rallied trainees' is the wordplay.
I cannot really understand how this works, but
'supporter' could be 'bra' (a bra gives support to breasts) and 'bra' is found in the answer.
an anagram of 'trainees' is 'inteaser' which is present in the answer.
This accounts for all the letters.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for brainteaser that I've seen before include "difficult exercise" , "It might be difficult" , "Puzzle" , "Puzzling thing" .)