The most common and most likely answer to this crossword clue is the 4 letter word LOCO
I've seen this crossword clue in Independent
L
O
C
O
More clues leading to the result LOCO
- See farm animal, with river rising, in plant that makes it mad?
- Can containing one hundred bananas
- Caught short, going in toilet that’s cracked
- Crazy for señorita one may pull online
- Cracked engine
- Catching cold, can 12?
- Engine off the rails
- Engine with a screw loose?
- Crazy, but often seen with motive?
- Cracked engine
Buddy explains!

The straight part
We know that "cracked" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case cracked = loco.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 LOCO mean?
LOCO adverb- A direction in written or printed music to be returning to the proper pitch after having played an octave higher or lower.
- A certain species of Astragalus or Oxytropis, capable of causing locoism.
- To poison with the loco plant; to affect with locoism.
- (by extension) To render insane.
- Crazy.
- Intoxicated by eating locoweed.
- A locomotive.