您可以将播放器的gamertag添加到查询参数中，例如：

echo "<a href='detailpage.php?player={$allPlayersItem['gamertag']}'>".$allPlayersItem['gamertag']."</a>";

然后在detailpage.php中，您可以编写：

$player = $_GET['player'] ?? '';
if ($player != '') {
     // display player details...
}

请注意，如果gamertag值可能包含特殊字符，那么在将其用作参数之前，应先urlencode值，即

echo "<a href='detailpage.php?player=" . urlencode($allPlayersItem['gamertag']) . "'>".$allPlayersItem['gamertag']."</a>";

首先，我建议您划分从数据库获取数据和呈现数据的责任。最常见的方法可能是遵循MVC模式。

类似的东西：

# Controller/PlayerController
final class PlayerController
{
    public function index(): Response
    {
        $players = [/* list of players to display. From the DB,for example*/];

        return $this->render('player/index.[blade|twig|php]',$players);
    }
}

# Views/player/index.php
<?php foreach ($players as $player): ?>
    <a href='detailpage.php'>" . <?= $player['gamertag']?> . "</a><br>"
<?php endforeach ?>

我建议您使用google研究并了解有关此主题的更多信息。