Loose horse in stall (5)
I believe the answer is:
baggy
'loose' is the definition.
(I've seen this in another clue)
'horse in stall' is the wordplay.
'horse' becomes 'gg' (geegee or GG is a childish term for a horse).
'in' indicates putting letters inside.
'stall' becomes 'bay' (I can't explain this - if you can you should give a lot more credence to this answer).
'gg' placed into 'bay' is 'BAGGY'.
Can you help me to learn more?
(Other definitions for baggy that I've seen before include "(Of clothes) loose and hanging" , "Bulging" , "Falling in loose folds" .)