Foolish about a girl, is possibly rooted to the spot (6)
I believe the answer is:
radish
'possibly rooted to the spot' is the definition.
I can't judge whether this defines the answer.
'foolish about a girl' is the wordplay.
'foolish' becomes 'rash' (I can't justify this - if you can you should give a lot more credence to this answer).
'about' means one lot of letters goes inside another.
'a girl' becomes 'Di'.
'rash' going around 'di' is 'RADISH'.
'is' acts as a link.
Can you help me to learn more?
(Other definitions for radish that I've seen before include "Sir had this vegetable" , "Edible small root" , "Bit of salad" , "Hard vegetable" , "Red cold salad ingredient" .)