After start of season frequently see weakness (4,4)
I believe the answer is:
soft spot
'weakness' is the definition.
(thesaurus)
'after start of season frequently see' is the wordplay.
'after' means one lot of letters go next to another.
'start of' says to take the initial letters.
'frequently' becomes 'oft' (I've seen this before).
'see' becomes 'spot' (I've seen this before**).
The initial letter of 'season' is 's'.
's' next to 'oft' is 'soft'.
'soft'+'spot'='SOFT SPOT'
(Other definitions for soft spot that I've seen before include "Feeling of affection towards person - not hard" , "Sentimental fondness" , "showing fondness" , "Emotional susceptibility" , "Affectionate weakness for (someone/something)" .)