The most common and most likely answer to this crossword clue is the 6 letter word OPPOSE
I've seen this crossword clue in The Guardian
O
P
P
O
S
E
More clues leading to the result OPPOSE
Buddy explains!

The straight part
We know that "resist" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case resist = oppose.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 OPPOSE mean?
OPPOSE verb- To attempt to stop the progression of; to resist or antagonize by physical means, or by arguments, etc.; to contend against.
- To object to.
- To present or set up in opposition; to pose.
- To place in front of, or over against; to set opposite; to exhibit.