rival, competitor

I beat them.

私は勝ちます

I beat my competitor.

私は競争相手に勝ちます

I beat my competitor at the stadium.

私は競技場で競争相手に勝ちます

I beat my competitor at the stadium on final day.

私は決勝の日に競技場で競争相手に勝ちます

I beat my competitor at the stadium with my teammates on final day.

私はチームの仲間たちと決勝の日に競技場で競争相手に勝ちます