I don't have any more insight about a head-to-head algorithm, but here's a better way of dealing with an arbitrary number of rule sets. Each rule is defined in a separate subroutine and an array dispatch table is used to evaluate them sequentially. If a rule's result is indeterminate, the next rule is tried. The following code is not rigorously tested, but should give you the idea.

my @teams = qw(mets yankees sox cubs braves cards);

my @rules = (
    \&wins,
    \&losses,
    \&headtohead,
    \&games,
    \&tiebreaker );

# games played, wins, losses, ties, tie breaker, teams defeated 
my %stats = (
    braves =>   [20, 18,  2, 0, 1, {yankees => 1, cubs => 1, etc => 1}
+ ],
    yankees =>  [20, 18,  2, 0, 2, {braves => 1}  ],
    mets =>     [20, 18,  2, 0, 3, {cubs => 1}    ],
    sox =>      [20,  8, 12, 0, 4, {yankees => 1} ],
    cubs =>     [20,  8, 12, 0, 5, {cards => 1}   ],
    cards =>    [20, 15,  5, 0, 6, {sox => 1}     ] );

my @standing = sort{ 
    my $cv;
    for (@rules){
        $cv = $_->($a, $b);
        last if $cv;
    }
    return $cv;
}@teams;

print "@teams\n";
print "@standing\n";

## The Rules:

sub wins{
    my ($a, $b) = @_;
    return $stats{$b}[1] <=> $stats{$a}[1];
}
sub losses{
    my ($a, $b) = @_;
    return $stats{$a}[2] <=> $stats{$b}[2];
}
sub headtohead{
    my ($a, $b) = @_;
    my $win = 0;
    $win-- if $stats{$a}[5]{$b};
    $win++ if $stats{$b}[5]{$a};
    return $win;
}
sub games{
    my ($a, $b) = @_;
    return $stats{$a}[0] <=> $stats{$b}[0];
}
sub tiebreaker{ 
    my ($a, $b) = @_;
    return $stats{$a}[4] <=> $stats{$b}[4];
}
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