{
      "id" : player:(some number)",
      "name" : "Martinez, Javi",
      "type" : "midfielder",
      "jersey_number" : 8,
      "position" : "Central defender"
    }

Document player = playersOnPitchHome.get(0);
       int i;
       for (i=0; i<playersOnPitchHome.size(); i++) {
           player = playersOnPitchHome.get(i);
           int numberTemp = (int) player.get("jersey_number"); //here
           if (numberTemp == playerNumber) break;
           if (i==(playersOnPitchHome.size()-1) && numberTemp != playerNumber) {
              throw new Exception ("there is no such player on the pitch");
          }

    }