Move over the sea, caught in a lot of foam (4)
I believe the answer is:
scud
'move over the sea' is the definition.
(to scud is to move quickly over the sea)
'caught in a lot of foam' is the wordplay.
'caught' becomes 'c' (cricket abbreviation).
'in' indicates putting letters inside.
'a lot of' means to remove the last letter (most of the word but not all of it).
'foam' becomes 'suds' (suds is a kind of foam).
'suds' with its last letter taken off is 'sud'.
'c' placed inside 'sud' is 'SCUD'.
(Other definitions for scud that I've seen before include "Hurry along (like clouds)" , "(Of a cloud) move very quickly" , "Sail swiftly before the wind - missile" , "(Of a cloud) be driven by the wind" , "Move quickly (as if running before a gale)" .)