The most common and most likely answer to this crossword clue is the 8 letter word CRINGING
I've seen this crossword clue in The Daily Telegraph
C
R
I
N
G
I
N
G
Buddy explains!

The straight part
We know that "behaving very humbly" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case behaving very humbly = cringing.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 CRINGING mean?
CRINGING verb- To shrink, cower, tense or recoil, as in fear, disgust or embarrassment.
- To bow or crouch in servility.
- To contract; to draw together; to cause to shrink or wrinkle; to distort.
- Act of one who cringes.