Foolish person gets a lump (4)
I believe the answer is:
clot
This clue is a double definition.
'foolish person' is the first definition.
(I've seen this before)
'a lump' is the second definition.
(I've seen this in another clue)
'gets' is the link.
(Other definitions for clot that I've seen before include "Idiot - congeal" , "Coagulate - fool" , "Mass of material" , "Silly billy" , "Thrombus - fool" .)