Leave oddly sick sheep (5)
I believe the answer is:
scram
'leave' is the definition.
(scramming is a kind of leaving)
'oddly sick sheep' is the wordplay.
'oddly' means one should take alternating letters.
'sheep' becomes 'ram' (ram is a kind of sheep**).
The alternating letters of 'sick' are 'sc'.
'sc'+'ram'='SCRAM'
(Other definitions for scram that I've seen before include "Beat it, get lost, go away" , "Go away quickly" , "Clear off!" , "Make oneself scarce" , "Scarper" .)