Couple of quagmires disrupting relative's firework (5)
I believe the answer is:
squib
'firework' is the definition.
(squib is a kind of firework)
'couple of quagmires disrupting relative's' is the wordplay.
'couple of quagmires' becomes 'qu' (I can't explain this - if you can you should believe this answer much more).
'disrupting' is an insertion indicator (inside letters 'disrupt' the flow of outside one).
'relative' becomes 'sib' (sib is a kind of relative).
'qu' placed into 'sib' is 'SQUIB'.
Can you help me to learn more?
(Other definitions for squib that I've seen before include "Small explosive, often damp" , "Small explosive, may be damp" , "piece of satire" , "Firework, burns with a fizzing noise" , "Firecracker" .)