Ambassador attending qualifying round (4)
I believe the answer is:
heat
'qualifying round' is the definition.
(I've seen this in another clue)
'ambassador attending' is the wordplay.
'ambassador' becomes 'he' (His or Her Excellency).
'attending' becomes 'at' (I've seen this in other clues).
'he'+'at'='HEAT'
(Other definitions for heat that I've seen before include "Vehemence" , "It's measured in therms" , "Preliminary race to qualify finalists" , "Warmth - passion" , "Level of spice" .)