The most common and most likely answer to this crossword clue is the 5 letter word ILEUS
I've seen this crossword clue in Financial Times
I
L
E
U
S
Buddy explains!

The straight part
We know that "Obstruction" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case obstruction = ileus.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 ILEUS mean?
ILEUS noun- (modern usage) Disruption of the normal propulsive ability of the gastrointestinal tract, due to failure of peristalsis.
- (broad definition, now rare) Disruption of the normal propulsive ability of the gastrointestinal tract from any cause.