reliever

noun
1
a thing or person that removes or reduces pain, feelings of worry or unhappiness, or a problem
مسکن, تسکین‌دهنده, آرام‌بخش
2
a pitcher(= the player who throws the ball) who enters the game in place of the previous pitcher
پرتاب‌گر تعویضی
Wilson began his major-league career as a reliever.
The manager often has relievers warming up when the game starts.