Bottleneck improvisation on record (6)
I believe the answer is:
logjam
'bottleneck' is the definition.
(I've seen this before)
'improvisation on record' is the wordplay.
'improvisation' becomes 'jam'.
'on' says to put letters next to each other.
'record' becomes 'log' (logging is a kind of recording).
'jam' after 'log' is 'LOGJAM'.
(Other definitions for logjam that I've seen before include "Major stoppage" , "bottleneck" , "blockage" , "deadlock" , "impasse" .)