The most common and most likely answer to this crossword clue is the 9 letter word DOORPOSTS
I've seen this crossword clue in The Guardian
D
O
O
R
P
O
S
T
S
Buddy explains!
The straight part
We know that "supporters in opening frame" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case supporters in opening frame = doorposts.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 DOORPOSTS mean?
DOORPOSTS noun- Doorjamb