Runner in central Greece at first looks beatable (4)
I believe the answer is:
elbe
'runner' is the definition.
(I have seen 'River of Germany ' mean 'elbe' so perhaps 'river' could also mean 'elbe')
'in central greece at first looks beatable' is the wordplay.
'in' indicates putting letters inside.
'central' indicates the central letters.
'at first' indicates taking the first letters.
The middle of 'greece' is 'ee'.
The initial letters of 'looks beatable' is 'lb'.
'ee' enclosing 'lb' is 'ELBE'.
(Other definitions for elbe that I've seen before include "It flows through Germany" , "Dresden/Hamburg river" , "German banker" , "A major German river" , "Current" .)