Below par when Arthur teed off - gripping end to game (5,3,7)
I believe the answer is:
under the weather
'below par' is the definition.
(thesaurus)
'when arthur teed off gripping end to game' is the wordplay.
'off' is an anagram indicator.
'gripping' means one lot of letters goes inside another.
'end to' suggests the final letters.
The last letter of 'game' is 'e'.
'when'+'arthur'+'teed'='whenarthurteed'
'whenarthurteed' with letters rearranged gives 'undrtheweather'.
'undrtheweather' going around 'e' is 'UNDER THE WEATHER'.
(Other definitions for under the weather that I've seen before include "Sick" , "Out of sorts" , "with clouds gathering overhead" , "Depressed" , "Sickening" .)