Become obstructed (4)
'become obstructed' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for clot that I've seen before include "medical problem" , "Fool; solidified blood" , "Coagulated blood; twit" , "Idiot - congeal" , "Thick lump - thick person" .)
(Other definitions for clog that I've seen before include "Become blocked with wooden-soled shoe" , "Wooden footwear" , "Obstruct the wooden shoe" , "Bung up" , "Block with wooden-soled shoe?" .)