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JavaScript

var i = [
   {
      "title":"New Jersey",
      "NFLteams":[
         {
            "Name":"Jets",
            "Conference":"AFC",
         },
         {
            "Name":"Giants",
            "Conference":"NFC",
         }
         ]
   },
   {
      "title":"Massachusetts",
      "NFLteams":[
         {
            "Name":"Patriots",
            "Conference":"AFC",
         }
         ]
   },
   {
      "title":"California",
      "NFLteams":[
         {
            "Name":"Raiders",
            "Conference":"AFC",
         },
         {
            "Name":"49ers",
            "Conference":"NFC",
         },
         {
            "Name":"Chargers",
            "Conference":"AFC",
         }
         ]
   }
];

var o = _.sortBy(i, function(team){ return team['NFLteams'].length }).reverse();
                                      
                                     console.log (o);