Hold tight when the sprag breaks (5)
I believe the answer is:
grasp
'hold tight' is the definition.
(thesaurus)
'the sprag breaks' is the wordplay.
'breaks' is an anagram indicator.
'sprag' anagrammed gives 'GRASP'.
'when' is the link.
(Other definitions for grasp that I've seen before include "Appreciation" , "Catch on" , "Hold tightly" , "Take firm hold" , "Seize firmly - or understand (5)" .)