"third-stringer" meaning in English

{
  "etymology_templates": [
    {
      "args": {
        "1": "en",
        "2": "third string",
        "3": "-er"
      },
      "expansion": "third string + -er",
      "name": "affix"
    }
  ],
  "etymology_text": "third string + -er.",
  "forms": [
    {
      "form": "third-stringers",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {},
      "expansion": "third-stringer (plural third-stringers)",
      "name": "en-noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "senses": [
    {
      "categories": [
        {
          "kind": "other",
          "name": "English entries with incorrect language header",
          "parents": [
            "Entries with incorrect language header",
            "Entry maintenance"
          ],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "English terms suffixed with -er",
          "parents": [],
          "source": "w"
        },
        {
          "kind": "topical",
          "langcode": "en",
          "name": "People",
          "orig": "en:People",
          "parents": [
            "Human",
            "All topics",
            "Fundamental"
          ],
          "source": "w"
        }
      ],
      "glosses": [
        "One who is a third string."
      ],
      "id": "en-third-stringer-en-noun-5H24rdEB",
      "links": [
        [
          "third string",
          "third string"
        ]
      ]
    }
  ],
  "word": "third-stringer"
}

{
  "etymology_templates": [
    {
      "args": {
        "1": "en",
        "2": "third string",
        "3": "-er"
      },
      "expansion": "third string + -er",
      "name": "affix"
    }
  ],
  "etymology_text": "third string + -er.",
  "forms": [
    {
      "form": "third-stringers",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {},
      "expansion": "third-stringer (plural third-stringers)",
      "name": "en-noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "senses": [
    {
      "categories": [
        "English countable nouns",
        "English entries with incorrect language header",
        "English lemmas",
        "English multiword terms",
        "English nouns",
        "English terms suffixed with -er",
        "en:People"
      ],
      "glosses": [
        "One who is a third string."
      ],
      "links": [
        [
          "third string",
          "third string"
        ]
      ]
    }
  ],
  "word": "third-stringer"
}