The most common and most likely answer to this crossword clue is the 4 letter word DUFF
I've seen this crossword clue in The Times
D
U
F
F
Buddy explains!

The straight part
We know that "Pants" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case pants = duff.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 DUFF mean?
DUFF noun- Dough.
- A stiff flour pudding, often with dried fruit, boiled in a cloth bag, or steamed.
- A pudding-style dessert, especially one made with plums.
- Decaying vegetable matter on the forest floor.
- Coal dust, especially that left after screening or combined with other small, unsaleable bits of coal.
- Fine and dry coal in small pieces, usually anthracite.
- A mixture of coal and rock.
- The bits left in the bottom of the bag after the booty has been consumed, like crumbs.
- Something spurious or fake; a counterfeit, a worthless thing.
- (1800s) An error.
- Worthless; not working properly, defective.
- The buttocks.
- To disguise something to make it look new.
- To alter the branding of stolen cattle; to steal cattle.
- (with "up") To beat up.
- To hit the ground behind the ball.
- A large frame drum, resembling a tambourine, used to accompany popular and classical music in the Middle East.