Certain of coming back with Oscar, initially the editor seemed pretty confident (10)
I believe the answer is:
surefooted
'confident' is the definition.
(I know that confident can be written as surefooted)
'certain of coming back with oscar initially' is the wordplay.
'certain' becomes 'sure' (synonyms).
'coming back' says the letters should be written backwards.
'with' means one lot of letters go next to another.
'oscar' becomes 'O' (phonetic alphabet: alpha, bravo, charlie etc.).
'initially' becomes 'ted' (I can't explain this - if you can you should believe this answer much more).
'of' reversed gives 'fo'.
'sure'+'fo'+'o'+'ted'='SUREFOOTED'
'the editor seemed pretty' 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?
(Another definition for surefooted that I've seen is " without any slip-up".)