Spot the bubble (6)
I believe the answer is:
seethe
'bubble' is the definition.
(I know that seethe is a type of froth)
'spot the' is the wordplay.
'spot' becomes 'see' (I've seen this in another clue).
'see'+'the'='SEETHE'
(Other definitions for seethe that I've seen before include "get very angry" , "Bubble away" , "Bubble gently like boiling water" , "Be livid" , "Boil; fume with suppressed rage" .)