$ranks = array(
    "derp" => 1,
    "herp" => 2,
    "master" => 3,
    "durr" => 4
    );

$array = array(
    0 => array(
        'name' => 'john',
        'points' => 10,
        'rank' => 'herp'
        ),
    1 => array(
        'name' => 'mike',
        'points' => 15,
        'rank => 'derp'
        )
    );

usort($array, function($a, $b) {
    if($a['rank'] == $b['rank']) return $b['points'] - $a['points'];
    return $b['rank'] - $a['rank'];
}