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 };