Conclude letter on Scrabble board will be unproductive (9)
I believe the answer is:
infertile
'unproductive' is the definition.
(associated in meaning)
'conclude letter on scrabble board' is the wordplay.
'conclude' becomes 'infer' (inferring is a kind of concluding).
'letter on scrabble board' becomes 'tile' (Scrabble is played with letter tiles).
'infer'+'tile'='INFERTILE'
'will be' acts as a link.
(Other definitions for infertile that I've seen before include "Barren" , "So can't father" , "Fruitless" , "Not productive" .)