The most common and most likely answer to this crossword clue is the 6 letter word UPWIND
U
P
W
I
N
D
Buddy explains!

The straight part
We know that "going against the flow" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case going against the flow = upwind.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 UPWIND mean?
UPWIND adjective- Exposed to the wind
- In the direction from which the wind is blowing
- To wind upwards.
- To wind up (a mechanism).