how to deal with inconsistent json fields in documents

I currently have a large JSON file which has to be stored in the backend (mongodb & Go) and consumed in the front end. I was wondering whether the 3rd field of the documents should be something like "Sub category" instead of the sport name from the 2nd field or whether this is possible as I was thinking this maybe hard to model and deserialise in a backend language due to inconsistency?

sample:

{
  "_id" : ObjectId("55c"),
  "Sport" : "Athletics ",
  "Athletics" : {
    ["Men's Individual", "Women's Individual", "Mixed Relay"]
   }
}

{
  "_id" : ObjectId("56c"),
  "Sport" : "Tennis",
  "Tennis" : ["Men's singles", "Women's singles", "Men's doubles", "Women's doubles", "Mixed doubles"]
}

{
  "_id" : ObjectId("57c"),
  "Sport" : "Swimming",
  "Swimming" : {
    "Men" : ["4×100 m relay", "4×200 m freestyle relay"],
    "Women" : ["4×100 m relay", "4×200 m freestyle relay"]
  }
}

I'd agree with the little voice telling you to go with "Sub-Category" instead of trying to deal with inconsistent types. Also, you should combine the 'mens' and 'womens' subcategories in Swimming similar to how you do it it in Tennis and Athletics. This will let you make better use of encoding/json's (and mgo/bson's) mapping features, but I wouldn't call it a 'backend language' problem - consistent data types should make your js (and other client code) nicer, too!

You can do that using json.RawMessage:

package main

import (
	"encoding/json"
	"fmt"
	"log"
)

func main() {
	type Color struct {
		Space string
		Point json.RawMessage // delay parsing until we know the color space
	}
	type RGB struct {
		R uint8
		G uint8
		B uint8
	}
	type YCbCr struct {
		Y  uint8
		Cb int8
		Cr int8
	}

	var j = []byte(`[
		{"Space": "YCbCr", "Point": {"Y": 255, "Cb": 0, "Cr": -10}},
		{"Space": "RGB",   "Point": {"R": 98, "G": 218, "B": 255}}
	]`)
	var colors []Color
	err := json.Unmarshal(j, &colors)
	if err != nil {
		log.Fatalln("error:", err)
	}

	for _, c := range colors {
		var dst interface{}
		switch c.Space {
		case "RGB":
			dst = new(RGB)
		case "YCbCr":
			dst = new(YCbCr)
		}
		err := json.Unmarshal(c.Point, dst)
		if err != nil {
			log.Fatalln("error:", err)
		}
		fmt.Println(c.Space, dst)
	}
}