Cause to crack (4)
I believe the answer is:
chap
'cause to crack' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for chap that I've seen before include "Fellow < makes > crack" , "Raw, cracked patch on skin" , "Become sore; fellow" , "we prefer not to have on hand" , "Split in skin" .)