The most common and most likely answer to this crossword clue is the 7 plus 6 letter word RUNNING BATTLE
I've seen this crossword clue in The Daily Telegraph
R
U
N
N
I
N
G
B
A
T
T
L
E
Buddy explains!
The straight part
We know that "Ongoing conflict between managers" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case ongoing conflict between managers = running battle.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.