my $hdata = <call that creates the struct>;
my ($rating, $bwurl) = 0;
foreach my $id ( keys %$hdata ) {
    if($hdata->{$id}{Season} == $seasonnum && $hdata->{$id}{Rating} > $rating){
         $rating = $hdata->{$id}{Rating};
         $bwurl  = $hdata->{$id}{BannerPath};
    }
}

##</code><code>##

use List::Util qw[ reduce ];
...
my $hdata = <call that creates the struct>;
my( $rating, $bwurl ) = @{ reduce{
    if( $hdata->{$b}{Season} == $seasonnum && $hdata->{$b}{Rating} > $a->[0] ){
        $a->[0] = $hdata->{$b}{Rating};
        $a->[1] = $hdata->{$b}{BannerPath}
    }
} [ 0, '' ], keys %hdata };