由于主力球员受伤，这位替补后卫终于获得了上场机会。

With the main players injured, the ___third-string defender finally got to play in the match.

由于主力球员受伤，教练不得不启用替补席上的第三选择。

With the star players injured, the coach had to rely on his ___third-string options from the bench.