Wanted to see knight in action (7)
I believe the answer is:
desired
'wanted' is the definition.
('desired' can be similar in meaning to 'wanted')
'knight in action' is the wordplay.
'knight' becomes 'sir' (I've seen this before).
'in' is an insertion indicator.
'action' becomes 'deed' (deed is a kind of action).
'sir' placed inside 'deed' is 'DESIRED'.
'to see' is the link.
(Other definitions for desired that I've seen before include "Wanted greatly" , "Had aspired to" , "Wanted strongly" , "much wished for" , "Sought after" .)