Occurring in irregular bursts (9)
I believe the answer is:
spasmodic
'occurring in irregular bursts' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for spasmodic that I've seen before include "Occasional" , "Intermittent" , "Occurring in irregular bursts" , "Done in short bursts" , "fitfully" .)