Knight said to run into battle for a fee (9)
I believe the answer is:
surcharge
'for a fee' is the definition.
(I have seen 'Excess fee ' mean 'surcharge' so perhaps 'fee' could also mean 'surcharge')
'knight said to run' is the wordplay.
'knight' becomes 'sir' (a knight has the title Sir).
'said' indicates a 'sounds like' (homophone) clue.
'to run' becomes 'charge' ().
'sir' is a homophone of 'sur'.
'sur'+'charge'='SURCHARGE'
'into battle' acts as a link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for surcharge that I've seen before include "Tax" , "Additional sum demanded" , "More to pay" , "additional amount" , "Additional payment" .)