Each jogger not half keen! (5)
I believe the answer is:
eager
'keen' is the definition.
(I've seen this in another clue)
'each jogger not half' is the wordplay.
'each' becomes 'ea' (abbreviation).
'not half' suggests halving the letters.
'jogger' with half the letters taken is 'ger'.
'ea'+'ger'='EAGER'
(Other definitions for eager that I've seen before include "Low platform" , "Earnest" , "Keen - enthusiastic" , "Excited by desire" , "Sharp" .)