The most common and most likely answer to this crossword clue is the 4 letter word BRAT
I've seen this crossword clue in Financial Times
B
R
A
T
More clues leading to the result BRAT
- Club welcoming rogue at first, ill-mannered child
- Cricketer accumulating runs, a spoilt youngster?
- Unruly youngster runs into club
- Black rodent irritating child
- Obnoxious child, born scoundrel
- Annoying child runs into club
- Nasty kid runs into club
- Young Simpson has change of heart ?- horrid kid!
- Black animal, one of a pack?
- Kid brother cheers up
Buddy explains!

The straight part
We know that "one of a pack" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case one of a pack = brat.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 BRAT mean?
BRAT noun- A child who is regarded as mischievous, unruly, spoiled, or selfish.
- A son or daughter (at any age) of an active military service member.
- A turbot or flatfish
- A rough cloak or ragged garment
- A coarse kind of apron for keeping the clothes clean; a bib.
- The young of an animal.
- Bratwurst
- A thin bed of coal mixed with pyrites or carbonate of lime.
- Acronym of Born, Raised, And Transferred.