Mufti Indian’s sporting endlessly (2,9)
I believe the answer is:
ad infinitum
'endlessly' is the definition.
(I've seen this before)
'mufti indian's sporting' is the wordplay.
'sporting' indicates an anagram.
'mufti'+'indian'='muftiindian'
'muftiindian' is an anagram of 'AD INFINITUM'.
(Other definitions for ad infinitum that I've seen before include "Endlessly, forever (Lat.)" , "Indefinitely" .)