Runs away from sullen elk (5)
I believe the answer is:
moose
'elk' is the definition.
(I know that elk can be written as moose)
'runs away from sullen' is the wordplay.
'runs' becomes 'r' (cricket abbreviation).
'away from' suggests deleting specific letters.
'sullen' becomes 'morose' (both mean miserable).
'morose' with 'r' removed is 'MOOSE'.
(Other definitions for moose that I've seen before include "Large US deer" , "North American deer" , "beasts" , "Large northern deer" , "Ungulate" .)