Failure, one caught in race (4)
I believe the answer is:
ruin
'failure' is the definition.
(I know that ruin is a type of failure)
'one caught in race' is the wordplay.
'one' becomes 'i' (Roman numeral).
'caught in' is an insertion indicator.
'race' becomes 'run' (running is a kind of racing).
'i' going within 'run' is 'RUIN'.
(Other definitions for ruin that I've seen before include "Physical collapse" , "Scotch" , "State of devastation and destruction" , "Destroy or bankrupt" , "Reduce to bankruptcy" .)