Big Lee, maybe about 51, fit to be chosen (8)
I believe the answer is:
eligible
'fit to be chosen' is the definition.
(I've seen this in another clue)
'big lee maybe about 51' is the wordplay.
'maybe' is an anagram indicator.
'about' means one lot of letters goes inside another.
'51' becomes 'LI' (Roman numerals).
'big'+'lee'='biglee'
'biglee' is an anagram of 'egible'.
'egible' going around 'li' is 'ELIGIBLE'.
(Other definitions for eligible that I've seen before include "Available, qualifying" , "Qualified or fit as bachelor may be" , "Qualified to be chosen, say a bachelor" , "Entitled, suitable" , "Fit to be chosen" .)