Setback as runs slip away (7)
I believe the answer is:
relapse
'setback' is the definition.
(I've seen this in another clue)
'runs slip away' is the wordplay.
'runs' becomes 'r' (cricket abbreviation).
'slip away' becomes 'elapse' (synonyms).
'r'+'elapse'='RELAPSE'
'as' is the link.
(Other definitions for relapse that I've seen before include "Failure to maintain a higher state" , "A return to illness" , "causing setback to recovery" , "Slide back into former condition as of illness (7)" , "Deteriorate in health" .)