Man possibly reading half of all the letters . . . (5)
I believe the answer is:
ralph
'man' is the definition.
(I've seen this before)
'reading half of all the letters' is the wordplay.
'reading' becomes 'r' (one of the traditional three R's of education).
'half of' means to take half the letters.
'all the letters' becomes 'alphabet'.
'alphabet' halved is 'alph'.
'r'+'alph'='RALPH'
'possibly' is the link.
(Other definitions for ralph that I've seen before include "Fellow's name" , "- Vaughan Williams, English composer" , "Chap" , "Man's name" , "___ Fiennes, English actor, b. 1962" .)