I’m not sure I follow what you’re code is trying to do, but try this and see if it gets you the result you need:
<?php
$gallery = get_field('event_gallery');
?>
<div>
<ul>
<?php foreach( $gallery as $image ): ?>
<li>
<img src="<?php echo esc_url($image['url']); ?>" alt="<?php echo esc_attr($image['alt']); ?>" />
</li>
<?php endforeach; ?>
</ul>
</div>
Just make sure your field returns format as image array.
