The most common and most likely answer to this crossword clue is the 8 letter word SLIPSHOD
I've seen this crossword clue in The Daily Telegraph
S
L
I
P
S
H
O
D
More clues leading to the result SLIPSHOD
- Loose underclothes? How foolish to pirouette!
- Careless mistakes lead to horrific overdose
- Careless mistakes with brickie’s equipment
- Careless errors by head office department
- Careless mistakes by brick carrier
- Careless errors by half-hearted criminal
- Edges in wearing shoes, being careless
- Slide, wearing shoes, being careless?
- Careless mistake with wearing shoes
- Careless fielders who’d dropped opener
Buddy explains!

The straight part
We know that "careless" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case careless = slipshod.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 SLIPSHOD mean?
SLIPSHOD adjective- Done poorly or too quickly; slapdash.
- Wearing slippers or similarly open shoes.