Too much foam: a drawback (7)
I believe the answer is:
surfeit
'too much' is the definition.
(a surfeit of something is too much of it)
'foam a drawback' is the wordplay.
I cannot quite understand how this works, but
'foam' could be 'surf' (I've seen this before) and 'surf' is found in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for surfeit that I've seen before include "Overindulge" , "it's more than one needs" , "Overindulgence" , "stuff, once" , "having had quite enough" .)