Beginning to develop the Knight's advancement (7)
I believe the answer is:
nascent
'beginning to develop' is the definition.
(I've seen this before)
'the knight's advancement' is the wordplay.
'the knight' becomes 'n' (chess).
'advancement' becomes 'ascent' (I've seen this before).
'n'+'ascent'='NASCENT'
(Other definitions for nascent that I've seen before include "Coming into existence" , "Sent can (anag.)" , "Starting to grow" , "being developed" , "Emerging, in the process of being born" .)