Refresh listbox when changing another

I am trying to create a system through listbox, that when selecting one, update the other.

One is EQUIPMENT and another is that of PLAYERS.

At the moment, I have a script with ajax and an example in php, but it does not work for me

This is the ajax script

     <script src="//ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js"></script>
    <script src="http://ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js"></script>


<script type="text/javascript">
$(document).ready(function(){
    $('#equipos').on('change',function(){

      var equipos = $(this).val();

      $.ajax({
        type:"POST", 
        dataType:'json',
        url : "prueba.php",
        data : { opcion: equipos },    
        success: function(response){
          alert("HOLA");
          $("#jugadores").html(response);
        },  
        error: function() {
          alert('Error occured');
        }
      });
    });
  });
</script>

And here is the PHP example that I have at the moment, the equipment listbox if it updates, but the player listbox does not.

<?php

 if(isset($_REQUEST["opcion"]))
 {
    $opciones = '<option value="0">"Elige el jugador"</option>';
    $conexion = new mysqli("localhost","root", "", "dartsfusion");
    $sqlCIU = "SELECT nom_j1, nom_j2, nom_j3, nom_j4, nom_j5, nom_j6, nom_j7, nom_j8 FROM equipos WHERE name_eq ='" . $_REQUEST['opcion'] . "'";
    $resCIU = $conexion->query($sqlCIU);
    while( $fila = $resCIU->fetch_array() )
    {
       $opciones.='<option value="'.$fila[0].'">'.$fila[0].'</option>';
    }

    // Liberar resultados
    mysqli_free_result($resCIU);

    // Cerrar la conexión
    mysqli_close($conexion);

    echo $opciones;
 }

?>

<!-- html con los select box -->

 <select name="equipos" id="equipos" class="form-control">
 <option value="" selected>Elige equipo</option>

<?php

$conexion = new mysqli("localhost","root", "", "dartsfusion");
$acentos = $conexion->query("SET NAMES 'utf8'");

$sqlPROV = "SELECT id_eq, name_eq FROM equipos";

if ($resPROV = $conexion->query($sqlPROV)) 
{
    while ($fila = $resPROV->fetch_row()) 
    {

    echo "<option value='" . $fila[0] . "' >" . $fila[1] . "</option>";    
    }
    $resPROV->close();
 }
?>
</select>
</div>

<div class="form-group">

  <select name="jugadores" id="jugadores" class="form-control">
  <option selected>Elige tu jugador</option>   
</select>

  </body>
</html>