$limit = -1;
$category = get_field('show_events_from_this_category');
$term = get_term_by('id', $category, 'tribe_events_cat'); // This shows a taxonomy ID

$arr = array('eventDisplay' => 'upcoming', 'posts_per_page' => $limit, 'tax_query' => array('taxonomy' => 'tribe_events_cat','field' => 'slug', 'terms' => $term->slug));

$posts = tribe_get_events( $arr );