Blocked when trickster made a joke, they say (9)
I believe the answer is:
congested
'blocked' is the definition.
(congesting is a kind of blocking)
'when trickster made a joke they say' is the wordplay.
I cannot quite see how this works, but
'when' could be 'on' (I've seen this in other clues) and 'on' is found within the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for congested that I've seen before include "Overcrowded, too full" , "Clogged up" .)