Said to love a bit of a flare-up! (4)
I believe the answer is:
oral
'said' is the definition.
(I've seen this before)
'love a bit of a flare-up' is the wordplay.
'love' becomes 'o' (love means zero in tennis).
'a bit of a flare' becomes 'lar' (I am not sure about this - if you are sure you should believe this answer much more).
'up' says the letters should be written in reverse (in down clue: letters go upwards).
'lar' back-to-front is 'ral'.
'o'+'ral'='ORAL'
'to' acts as a link.
Can you help me to learn more?
(Other definitions for oral that I've seen before include "Mouth-related" , "Spoken test" , "By word of mouth, like some exams" , "Exam using speech" , "Vocal test" .)