The most common and most likely answer to this crossword clue is the 9 letter word BREASTING
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Buddy explains!

The straight part
We know that "Manfully opposing" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case manfully opposing = breasting.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does BREASTING mean?
BREASTING verb- To push against with the breast; to meet full on, oppose, face.
- To reach the top (of a hill).
- To debreast.
- The curved channel in which a breastwheel turns.