The most common and most likely answer to this crossword clue is the 8 plus 1 plus 3 letter word STARTING A ROW
I've seen this crossword clue in The Daily Telegraph
S
T
A
R
T
I
N
G
A
R
O
W
Buddy explains!
The straight part
We know that "Causing trouble/putting one’s oar in" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case causing trouble/putting one’s oar in = starting a row.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.