After, say, golf, he notices experts (8)
I believe the answer is:
eggheads
'experts' is the definition.
(an egghead is a clever person)
'after say golf he notices' is the wordplay.
'after' says to put letters next to each other.
'say' becomes 'eg' (short for 'exempli gratia', 'for example' in Latin).
'golf' becomes 'g' (phonetic alphabet: alpha, bravo, charlie etc.).
'notices' becomes 'ads' (advertisements).
'eg' put next to 'g' is 'egg'.
'egg'+'he'+'ads'='EGGHEADS'
(Other definitions for eggheads that I've seen before include "Intellectuals with ovoid craniums" , "TV quiz show" , "academic talents" , "Intellectuals (colloq.)" , "Slangy intellectuals with lofty domes" .)