Saving metabox content not working

The main problem is you’re not echoing names of your fields. Like <input type="text" name="<? 'jugador_' . $contador ?>" should be <input type="text" name="<? echo 'jugador_' . $contador ?>"

Still, I have a better suggestion. You can use arrays in your form submission. So your metabox callback function should look like this:

function mock_metabox() {
    global $post;
    // Nonce field
    wp_nonce_field( basename( __FILE__ ), 'mock_fields' );
    // init counter for meta array
    $selecciones = get_post_meta( $post->ID, '_seleccion', true );
    $equipos = get_post_meta( $post->ID, '_equipo', true );
    $equiposog = get_post_meta( $post->ID, '_equipoog', true );

    // Output the fields
    ?>
    <h3> Informacion del Mock </h3>
    <table>
    <tr>
    <th> # </th>
    <th> Jugador </th>
    <th> Equipo </th>
    <th> Equipo Original </th>
    </tr>

    <?

    $contador = 1;

    $teams = get_posts( array(
            'post_type' => 'team',
            'orderby'   => 'title',
            'order'  => 'ASC',
            'numberposts' => -1,
            'post_status' => 'publish'
        ) );

    while ( $contador <= 60 ){
        $v_jugador = isset( $selecciones[$contador-1] ) ? $selecciones[$contador-1] : '';
        $v_equipo = isset( $equipos[$contador-1] ) ? $equipos[$contador-1] : '';
        $v_equiposog = isset( $equiposog[$contador-1] ) ? $equiposog[$contador-1] : '';
        ?>
        <tr>
            <td><?php echo $contador ?></td>
            <td><input type="text" name="jugador[]" value="<?php echo $v_jugador; ?>" />
            <td><select name="equipo[]"><?
            foreach ( $teams as $team ) { ?>
                <option value="<?php echo $team->ID; ?>" <?php selected( $v_equipo, $team->ID ); ?> > <?php echo $team->post_title; ?> </option> <? } ?> </select> </td>
            <td><select name="equipoog[]"><?
            foreach ( $teams as $team ) { ?>
                <option value="<?php echo $team->ID; ?>" <?php selected( $v_equiposog, $team->ID ); ?>  > <?php echo $team->post_title; ?> </option> <? } ?> </select> </td>
            <? $contador++; ?>
        </tr>
        <?php } ?>
    </table>
    <?
}

And the updating function to this:

function mock_save_meta_box_data( $post_id ){
    // verify taxonomies meta box nonce
    if ( !isset( $_POST['mock_fields'] ) || !wp_verify_nonce( $_POST['mock_fields'], basename( __FILE__ ) ) ){
        return;
    }
    // return if autosave
    if ( defined( 'DOING_AUTOSAVE' ) && DOING_AUTOSAVE ){
        return;
    }
    // Check the user's permissions.
    if ( ! current_user_can( 'edit_post', $post_id ) ){
        return;
    }
    // guarda tipo traspaso
    if ( isset( $_POST['jugador'] ) ) {
        update_post_meta( $post_id, '_seleccion', $_POST['jugador'] );
    }
    if ( isset( $_POST['jugador'] ) ) {
        update_post_meta( $post_id, '_equipo', $_POST['equipo'] );
    }
    if ( isset( $_POST['jugador'] ) ) {
        update_post_meta( $post_id, '_equipoog', $_POST['equipoog'] );
}

add_action( 'save_post_mock', 'mock_save_meta_box_data' );

Give it a try.

Edit: Don’t use checked() in select field’s options. Use selected() function.