Compare two numeric custom fields

I think something like this, but not tested, and my SQL-foo is rather weak:

    $test = $wpdb->get_col( $wpdb->prepare(
    "
    SELECT DISTINCT    $wpdb->posts.*
    FROM               $wpdb->posts
    INNER JOIN         $wpdb->postmeta AS mt1 ON (
         wp_posts.ID = $wpdb->postmeta.post_id
    )
    WHERE              $wpdb->postmeta.meta_key = 'goals-made'
    AND(               mt1.meta_key = 'goals-against'
        AND            CAST($wpdb->postmeta.meta_value AS INT) > CAST(mt1.meta_value AS INT)
    )

    "
));

This should return a list of post_ids that you can then process. But then again, it might just fail miserably.

If I was in your situation, I'd used a different approach.

Simply add an hidden meta field automatically when goals_made is updated.

E.g.

add_action('updated_postmeta', 'update_goal_made', 20, 4);

function update_goal_made( $meta_id, $object_id, $meta_key, $_meta_value ) {
  if ( $meta_key != 'goals-made') return; // run only when update meta 'goals-made'
  // get the goals-against for post
  $against = get_post_meta($object_id, 'goals-against', true) ? : 1;
  // if 'goals-made' > 'goals-against' create/update a field '_goals-won' setted to 1
  if ( intval($_meta_value) > intval($against) ) {
    update_post_meta($object_id, '_goals-won', '1');
  } else {
    // if not delete '_goals-won' post meta (if exists)
    delete_post_meta($object_id, '_goals-won');
  }
}

Now to retrieve the posts where _goals-won exists, simply run a meta query:

$args = (
  'posts_per_page' => -1,
  'meta_query' => array( array('meta_key'=>'_goals-won') )
);
$won_posts = get_posts($args);

EDIT

After some works on GhostToast answer I can give you also the right SQL query to get the same result.

global $wpdb;
$won_posts = $wpdb->get_results( "
    SELECT $wpdb->posts.* 
        FROM $wpdb->posts
    INNER JOIN $wpdb->postmeta AS mt1 ON ( $wpdb->posts.ID = mt1.post_id )
    INNER JOIN $wpdb->postmeta AS mt2 ON ( $wpdb->posts.ID = mt2.post_id )
    WHERE mt1.meta_key = 'goals-made' 
        AND ( 
            mt2.meta_key = 'goals-against'
            AND CAST( mt1.meta_value AS UNSIGNED ) > CAST( mt2.meta_value AS UNSIGNED )
        )
    GROUP BY $wpdb->posts.ID
" );

Side note:

If someone write the SQL statement that handle your request, sure that SQL statement will be less performant then the simplest meta query like the first posted.

Hope I didn't understand the question wrong :)

$results = new WP_Query( array(
    'post_type'  => 'matches',
    'meta_query' => array(
        array(
            'key'     => 'goals-made',
            'value'   => (int) get_post_meta( get_the_ID(), 'goals-against',  true ),
            'type'    => 'INT',
            'compare' => ">",
        )
    ),
) );
if ( $results->have_posts() )
{
    while ( $results->have_posts() )
    {
        the_post();
        var_dump( $GLOBALS['post'] );
    }
}

As we don't know from where you're doing this query, simply replace get_the_ID() inside get_post_meta() with the retrieved ID of the posts you want to compare against.