Good scope offered by opening on board (6)
I believe the answer is:
gambit
'opening on board' is the definition.
(opening move in chess)
'good scope' is the wordplay.
'good' becomes 'g' (abbreviation).
'scope' becomes 'ambit' (synonyms).
'g'+'ambit'='GAMBIT'
'offered by' acts as a link.
(Other definitions for gambit that I've seen before include "Opening sacrifice made in chess game" , "Initial move found in bag, Tim" , "Stratagem in chess" , "opening on board" , "Sacrificial chess opening" .)