Something afoot that may wreck boats (5)
I believe the answer is:
sabot
'something afoot that' is the definition.
I can't judge whether this definition defines the answer.
'wreck boats' is the wordplay.
'wreck' is an anagram indicator.
'boats' anagrammed gives 'SABOT'.
'may' is the link.
Can you help me to learn more?
(Other definitions for sabot that I've seen before include "French clog" , "Wooden clog" , "French wooden shoe" , "This from last" , "Boast (anag) - shoe" .)