noun
competitor; contestant; player; athlete
General term for a person who participates in a competition, sports event, or game. Can refer to both amateur and professional participants.
彼はオリンピックの競技者として金メダルを取った。
He won a gold medal as an Olympic competitor.
競技者はスタートラインに並んだ。
The contestants lined up at the starting line.
参加者 means 'participant' in a general sense, including non-competitive events. 競技者 specifically implies a competitive setting.
Compound of 競技 (competition, match) and 者 (person). The reading is standard on'yomi.