Jumped when the plate broke (5)
I believe the answer is:
leapt
'jumped' is the definition.
(I've seen this before)
'the plate broke' is the wordplay.
'broke' is an anagram indicator.
'plate' is an anagram of 'LEAPT'.
'when' acts as a link.
(Other definitions for leapt that I've seen before include "Jumped, sprang" , "Took off" , "Made spring" , "gone up dramatically" , "rose fast" .)