One involved in a replay? (6)
I believe the answer is:
player
'one' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how they can define each other.
'involved in a replay?' is the wordplay.
'involved in' is an anagram indicator (involved can mean complex or confusing).
'replay' is an anagram of 'PLAYER'.
Can you help me to learn more?
(Other definitions for player that I've seen before include "Performer" , "powerful participant" , "Batsman perhaps" , "Participant in sport or game" , "Competitor; musician" .)