The most common and most likely answer to this crossword clue is the 6 letter word RODEOS
R
O
D
E
O
S
Buddy explains!

The straight part
We know that "stock round-ups" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case stock round-ups = rodeos.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 RODEOS mean?
RODEOS noun- A gathering of cattle to be branded.
- A North American sport involving skills with horses, cows and other livestock.
- An entertainment event associated with the sport.