The most common and most likely answer to this crossword clue is the 3 letter word MUD
I've seen this crossword clue in The Guardian
M
U
D
More clues leading to the result MUD
- Slander at first, most unfair detraction
- Managing Director crosses union leader, getting bad name
- Dirt making uniforms dirty, primarily
- Greek character died in wet earth
- Muck in mound regularly removed
- Bad name Greek character finally earned?
- Malicious utterance damaging leaders, perhaps
- Greek character died in sludge
- Female invited into garden not wanting a soft soil
- Greek character, police officer, last person to abuse
Buddy explains!

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 MUD mean?
MUD noun- A mixture of water and soil or fine grained sediment.
- A plaster-like mixture used to texture or smooth drywall.
- (construction industry slang) Wet concrete as it is being mixed, delivered and poured.
- Willfully abusive, even slanderous remarks or claims, notably between political opponents.
- Money, dough, especially when proceeding from dirty business.
- (gay sex) Stool that is exposed as a result of anal sex.
- A particle less than 62.5 microns in diameter, following the Wentworth scale
- A black person.
- Drilling fluid.
- Coffee.
- To make muddy or dirty; to apply mud to (something).
- To make turbid.
- To go under the mud, as an eel does.
- To participate in a MUD or multi-user dungeon.