public class Userstrafe implements CommandExecutor {

    public boolean onCommand(CommandSender sender, Command cmd, String label, String[] args) {
        Player p = null;
        if (args.length == 0) {
            sender.sendMessage("§cBenutze: §a/strafe <Spielername>");
            return true;
        }
        if (args.length == 1) {
            if (sender instanceof Player) {
                p = (Player) sender;
            }
        } else {
            String name = args[0];
            p = Bukkit.getPlayer(name);
        }
        if (p == null) {
            sender.sendMessage("§cDer Spieler ist nicht online!");
            return true;
        }
//      p.setFireTicks(20 * 900);
        p.addPotionEffect(new PotionEffect(PotionEffectType.BLINDNESS, 20 * 900, 5));
        p.addPotionEffect(new PotionEffect(PotionEffectType.CONFUSION, 20 * 900, 5));
        p.addPotionEffect(new PotionEffect(PotionEffectType.SLOW, 20 * 900, 3));
        sender.sendMessage("§2Der Spieler §e" + p.getName() + " §2wurde bestraft!");
        return false;
    }

}