Runs are hard to come by (4)
I believe the answer is:
rare
'hard to come by' is the definition.
'runs are' is the wordplay.
'runs' becomes 'r' (cricket abbreviation).
'r'+'are'='RARE'
(Other definitions for rare that I've seen before include "Unusual - exquisite" , "Bloody (of steaks)" , "like gold dust" , "Seldom seen or met" , "Rear up, being scarce" .)