functions.php

<?php
// Add this to your functions.php file to create a venue query that queries venues in order of number of events.
// You may need to add a limit statement if you want more events to be returned than the default for the query.
add_filter( 'pre_get_posts', 'my_function_to_get_venues_by_event_numbers', 10, 1 );
function my_function_to_get_venues_by_event_numbers( $query ) {
	$post_type = (array) $query->query_vars['post_type'];
  	if ( !is_single() && $post_type == array( TribeEvents::VENUE_POST_TYPE) ) {
		add_filter( 'posts_fields', 'my_posts_fields_for_venues_function', 20, 1 );
		add_filter( 'posts_join', 'my_posts_join_for_venues_function', 20, 1 );
		add_filter( 'posts_where', 'my_posts_where_for_venues_function', 20, 1 );
		add_filter( 'posts_groupby', 'my_posts_group_by_for_venues_function', 20, 1 );
		add_filter( 'posts_orderby', 'my_posts_order_by_for_venues_function', 20, 1 );
	}
	return $query;
}

function my_posts_fields_for_venues_function( $fields ) {
	global $wpdb;
	$fields = "{$wpdb->posts}.*, count(wp_postmeta.meta_value) as num_events";
	return $fields;
}

function my_posts_where_for_venues_function( $where ) {
	global $wpdb;
	$where = " AND {$wpdb->posts}.post_type = '" . TribeEvents::VENUE_POST_TYPE ."' AND ({$wpdb->posts}.post_status = 'publish' OR {$wpdb->posts}.post_status = 'private') AND {$wpdb->postmeta}.meta_key = '_EventVenueID'";
	return $where;
}

function my_posts_group_by_for_venues_function( $group ) {
	global $wpdb;
	$group = " {$wpdb->postmeta}.meta_value ";
	return $group;
}

function my_posts_order_by_for_venues_function( $order ) {
	$order = ' num_events DESC';
	return $order;
}

function my_posts_join_for_venues_function( $join ) {
	global $wpdb;
	$join = " INNER JOIN wp_postmeta ON (wp_posts.ID = {$wpdb->postmeta}.meta_value)";
	return $join;
}