limit_tckt_qty.php

<?php 
/* Tribe, limit ticket qty */
function tribe_limit_tickets() { 
	?>
    
    <script type="text/javascript">
    	jQuery(document).ready( function( $ ) {
    		// do this if tickets available
    		if ( $('.tribe-events-tickets').length ) {
    			// set max qty to 1
    			$('.tribe-events-tickets .tribe-ticket-quantity').attr('max', 1);
    			// run on input change
    			$('.tribe-events-tickets .tribe-ticket-quantity').change ( function ( ) {
    				// don't run the manually triggered change event
    				if ( $(this).val() == 0 ) return;
    				// make sure it's not more than 1
    				if ( $(this).val() > 1 ) $(this).val(1);
    				// change all inputs but this to 0
    				// manually trigger the change event so available stock gets updated
    				$('.tribe-events-tickets .tribe-ticket-quantity').not( $(this) ).val(0).change();
    			});
    			// add a oninput event
    			$('.tribe-events-tickets .tribe-ticket-quantity').on('input', function (e) {
    				$(this).change();
    			});
    		}
    	});
    </script>

    <?php
}
add_action('wp_head', 'tribe_limit_tickets');