Sandpiper in difficulty (4)
I believe the answer is:
knot
I believe this is a double definition.
'sandpiper' is the first definition.
(knot is a kind of sandpiper)
'difficulty' is the second definition.
(I've seen this before)
'in' acts as a link.
(Other definitions for knot that I've seen before include "Shore bird, tangle" , "Shore bird; cluster" , "that's sometimes in wood" , "Unit of speed in water" , "Fastening - unit of speed" .)