What is the meaning of reliever?

noun

• Someone who takes the place of another (as when things get dangerous or difficult. )
  • usage: "the star had a stand-in for dangerous scenes"; "we need extra employees for summer fill-ins"
  • synonyms: stand-in, substitute, relief, backup, backup man, fill-in
• A person who reduces the intensity (e. G., of fears) and calms and pacifies.
  • usage: "a reliever of anxiety"; "an allayer of fears"
  • synonyms: allayer, comforter
• A pitcher who does not start the game.
  • synonyms: relief pitcher, fireman