Inflames one curiously when only two out of four competitors play it (9)
I believe the answer is:
semifinal
'only two out of four competitors play it' is the definition.
I can't judge whether this defines the answer.
'inflames one curiously' is the wordplay.
'one' becomes 'i' (Roman numeral).
'curiously' indicates anagramming the letters.
'inflames'+'i'='inflamesi'
'inflamesi' anagrammed gives 'SEMIFINAL'.
'when' is the link.
Can you help me to learn more?
(Other definitions for semifinal that I've seen before include "Tie" , "big game" , "Competitive match" , "big match" , "Penultimate cup game" .)