Displaying JSON data in a ListView only displays the first element in the Array

I am doing a simple project in which I can firstly get JSON data from my database and then display it in a listview in my andorid application. I have the first part working fine as I can see that all the JSON data is there, however only the first element in the array is being displayed in my listview. Was hoping anyone could help as I am unsure as to where I cam going wrong. Thanks

PickPlayerActivity.java

public class PickPlayerActivity extends AppCompatActivity {


String json_string;
JSONObject jsonObject;
JSONArray jsonArray;
PlayerAdapter playerAdapter;
ListView listview;


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_pick_player);
    listview = (ListView) findViewById(R.id.listview);
    playerAdapter = new PlayerAdapter(this, R.layout.row_layout);
    listview.setAdapter(playerAdapter);
    json_string = getIntent().getExtras().getString("json_data");

    try {
        jsonObject = new JSONObject(json_string);
        jsonArray = jsonObject.getJSONArray("server_response");
        int count = 0;
        String firstname, surname, position;

        while(count<jsonObject.length()){

            JSONObject jo = jsonArray.getJSONObject(count);

            firstname = jo.getString("firstname");
            surname = jo.getString("surname");
            position = jo.getString("position");


            Players players = new Players(firstname, surname, position);

            playerAdapter.add(players);
            count ++;


        }


    } catch (JSONException e) {
        e.printStackTrace();
    }


}
}

activity_pick_player.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context="testproject.PickPlayerActivity">


<ListView
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:id="@+id/listview"

    />

row_layout.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent" android:layout_height="75dp">


<TextView

    android:layout_height="match_parent"
    android:layout_width="120dp"
    android:id="@+id/tx_firstname"
    android:layout_alignParentLeft="true"
    android:text="firstname"
    android:gravity="center"
    android:textAppearance="?android:textAppearanceLarge">

</TextView>

<TextView

    android:layout_height="match_parent"
    android:layout_width="120dp"
    android:id="@+id/tx_lastname"
    android:layout_toRightOf="@+id/tx_firstname"
    android:text="surname"
    android:gravity="center"
    android:textAppearance="?android:textAppearanceLarge">

</TextView>

<TextView

    android:layout_height="match_parent"
    android:layout_width="120dp"
    android:id="@+id/tx_position"
    android:layout_toRightOf="@+id/tx_lastname"
    android:text="position"
    android:gravity="center"
    android:textAppearance="?android:textAppearanceLarge">

</TextView>

players.java

public class Players {

private String position, firstname, lastname;

public Players(String firstname, String lastname, String position){

    this.setFirstname(firstname);
    this.setLastname(lastname);
    this.setPosition(position);

}

public String getFirstname(){
    return firstname;
}

public void setFirstname(String firstname)
{
    this.firstname = firstname;
}


public String getLastname() {
    return lastname;
}

public void setLastname(String lastname) {
    this.lastname = lastname;
}

public String getPosition() {
    return position;
}

public void setPosition(String position) {
    this.position = position;
}
}

PlayerAdapter.java

public class PlayerAdapter extends ArrayAdapter {

List list = new ArrayList();

public PlayerAdapter(Context context, int resource){
    super(context, resource);

}


public void add(Players object) {
    super.add(object);
    list.add(object);
}

@Override
public int getCount() {
    return list.size();
}

@Override
public Object getItem(int position) {
    return list.get(position);
}


@Override
public View getView(int position, View convertView, ViewGroup parent) {
    View row;
    row = convertView;
    PlayerHolder playerHolder;
    if (row==null){
        LayoutInflater layoutInflater = (LayoutInflater) this.getContext().getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        row = layoutInflater.inflate(R.layout.row_layout,parent,false);
        playerHolder = new PlayerHolder();
        playerHolder.tx_firstname = (TextView) row.findViewById(R.id.tx_firstname);
        playerHolder.tx_lastname = (TextView) row.findViewById(R.id.tx_lastname);
        playerHolder.tx_position = (TextView) row.findViewById(R.id.tx_position);
        row.setTag(playerHolder);

    }
    else{
        playerHolder = (PlayerHolder) row.getTag();


    }
    Players players = (Players) this.getItem(position);
    playerHolder.tx_firstname.setText(players.getFirstname());
    playerHolder.tx_lastname.setText(players.getLastname());
    playerHolder.tx_position.setText(players.getPosition());

    return row;
}


class PlayerHolder{

    TextView tx_firstname, tx_lastname, tx_position;

}

}