Worried RAF leaders for instance make fighters stand by (6)
I believe the answer is:
affirm
'fighters stand by' is the definition.
I can't tell whether this definition defines the answer.
'worried raf leaders for instance make' is the wordplay.
'worried' indicates anagramming the letters (worry can mean to interfere with or disturb).
'leaders' says to take the initial letters.
The first letters of 'for instance make' is 'fim'.
'raf'+'fim'='raffim'
'raffim' with letters rearranged gives 'AFFIRM'.
Can you help me to learn more?
(Other definitions for affirm that I've seen before include "Make a formal declaration (rather than an oath)" , "Declare one's commitment (to)" , "Publicly state" , "State as a fact, assert" , "Substantiate" .)