The actors were first to have moved on board (7)
I believe the answer is:
castled
'have moved on board' is the definition.
(I've seen this before)
'the actors were first' is the wordplay.
'the actors' becomes 'cast' (group of actors).
'were first' becomes 'led'.
'cast'+'led'='CASTLED'
'to' acts as a link.
(Other definitions for castled that I've seen before include "made move in game" , "have moved on board" , "defensive move" , "Made a chess move" , "moved to protect king" .)