The most common and most likely answer to this crossword clue is the 8 letter word STRAYING
I've seen this crossword clue in Financial Times
S
T
R
A
Y
I
N
G
More clues leading to the result STRAYING
- It's smart catching fish that's drifting
- Errant man caught in police operation
- Distracted stingray wandering off
- Going off fish netted in swindle
- Going off beam, taken in by confidence trick
- Going off course, runs into the remaining
- Errant fish caught in sneaky trap
- Musician goes round narrow beam of light that’s out of place?
- Stingray swimming off course
Buddy explains!

The straight part
We know that "Errant" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case errant = straying.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 STRAYING mean?
STRAYING verb- To wander, as from a direct course; to deviate, or go out of the way.
- To wander from one's limits; to rove or roam at large; to go astray.
- To wander from the path of duty or rectitude; to err.
- To cause to stray.
- The act of one who strays; deviation or sin - often sexual infidelity.