Hear of snag in contract (5)
I believe the answer is:
catch
I believe this clue is a triple definition!
'hear of' is the first definition.
(catching is a kind of hearing of)
'snag' is the second definition.
(I've seen this before)
'in' is a link.
'contract' is the third definition.
(to catch an illness is to contract it)
(Other definitions for catch that I've seen before include "Capture; hidden problem" , "Discover" , "Accurately detect" , "Hidden drawback" , "Book by Joseph Heller" .)