The most common and most likely answer to this crossword clue is the 11 letter word ADVENTUROUS
I've seen this crossword clue in The Guardian
A
D
V
E
N
T
U
R
O
U
S
More clues leading to the result ADVENTUROUS
Buddy explains!

The straight part
We know that "reckless" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case reckless = adventurous.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 ADVENTUROUS mean?
ADVENTUROUS adjective- (of a person) Inclined to adventure; willing to incur risks; prone to embark in hazardous enterprise; rashly daring.
- (of an act or product) Full of hazard; attended with risk; exposing to danger; requiring courage; rash.