The most common and most likely answer to this crossword clue is the 7 letter word PRANCER
I've seen this crossword clue in The Guardian
P
R
A
N
C
E
R
More clues leading to the result PRANCER
- Swaggering customer who’s on the pull at Christmas?
- Reindeer quietly scampered round sports ground
- Springer CPR near useless
- Vixen’s crony, one engaged in capers
- Lively horse, after quiet start, sprinted — almost sure winner
- Heartless poacher has rumoured solution to reindeer that can fly
- Fled cold, stopping for each North Pole flyer?
- Reindeer managed to be arrested by Constable Queen
- Pressure on steeplechaser to get new horse
Buddy explains!

The straight part
We know that "Vixen’s crony/Vixen’s crony/one engaged in capers/one engaged in capers" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case vixen’s crony/vixen’s crony/one engaged in capers/one engaged in capers = prancer.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.