Spots the right tree (4)
I believe the answer is:
rash
'spots' is the definition.
(I've seen this before)
'right tree' is the wordplay.
'right' becomes 'r' (common abbreviation).
'tree' becomes 'ash' (ash is a kind of tree).
'r'+'ash'='RASH'
'the' is the link.
(Other definitions for rash that I've seen before include "Impulsive - eruption" , "Precipitate" , "Red patch on skin" , "Hasty; skin disorder" , "Ill-considered - outbreak" .)