Keelhaul a sister over some hemp (5)
I believe the answer is:
sisal
'hemp' is the definition.
(I've seen this in another clue)
'keelhaul a sister over some' is the wordplay.
'some' says the answer is hidden in the clue.
'over' is a reversal indicator.
'lasis' is hidden in the letters of 'keelhaul a sister'.
'lasis' back-to-front is 'SISAL'.
(Other definitions for sisal that I've seen before include "Plant producing rope" , "Strong rope fibre" , "Type of fibre" , "Fibrous plant used for rope" , "Rope fibre from leaves of tropical plant" .)