The most common and most likely answer to this crossword clue is the 6 letter word JAMMED
I've seen this crossword clue in Financial Times
J
A
M
M
E
D
More clues leading to the result JAMMED
Buddy explains!

The straight part
We know that "blocked" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case blocked = jammed.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 JAMMED mean?
JAMMED verb- To get something stuck in a confined space.
- To brusquely force something into a space; cram, squeeze.
- To cause congestion or blockage. Often used with "up"
- To block or confuse a broadcast signal.
- To throw a pitch at or near the batter's hands.
- To play music (especially improvisation as a group, or an informal unrehearsed session).
- To injure a finger or toe by sudden compression of the digit's tip.
- To attempt to score points.
- To bring (a vessel) so close to the wind that half her upper sails are laid aback.
- To give up on a date or some joint endeavour; stand up, chicken out, jam out.
- Stuck.
- Overcrowded; congested