Hashes and arrays are the same in array context. Try print join(", ", @_);at the beginning of your sub to see the effect.

I suggest passing references instead of hashes:

sub count_orientation {
    my $ref = shift;
    my $x = shift;
    my $y = shift;
    $x->{$ref}{amount}++;
    if ($y->{$ref}{orientation} eq "for"){
        $x->{$ref}{amountFor}++;
    } else {
        $x->{$ref}{amountRev}++;
    }
}
&count_orientation ($ref_end, \%error_start, \%score);
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Always remember that you're working on your original hashes when using references:

sub foo {
 my $hashref = shift;
 delete $hashref->{a};
 print keys %$hashref;
}
%x = (a => 1, b => 2);
foo(\%x);
print $x{a};
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using amperstand &func() ignores prototypes, so use func ...; instead

Or forget about prototypes and use  func3scalars( $scalar, \%two, \%three )

See Modern Perl: the free book

sub count_orientation($ \% \%){
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I was a bit surprised to find that spaces in a prototype declaration are accepted. A quick perusal of the perlsub documentation for ActiveState 5.8.9 and Strawberries 5.10.1 and 5.12.3 reveals no mention of whitespace. Ya learn somethin' every day.

The general consensus regarding prototypes seems to be that they were a good idea that was only 60%-80% baked, and that one should probably not use them unless one knows exactly how they work; the fact that Jaapx is calling a prototyped function in such a way as to defeat prototyping suggests he or she does not.

Avoid prototypes unless you really need to use them; they're not like argument/parameter lists in other languages (frankly I think your use here will confuse anyone reading your code!).

Instead, just pass references to the hashes. Thus:

sub count_orientation {
    my $ref = shift;
    my %x = %{(shift)};    # this is still correct!
    my $y = %{(shift)};
    # ...
}

count_orientation($x, \%error_start, \%score);
# or: count_orientation($x, {%error_start}, {%score});
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sub report {
    our %hash1; local *hash1 = $_[0];
    our %hash2; local *hash2 = $_[1];
    our %hash3; local *hash3 = $_[2];
    
    my $othervar1 = $_[3];
    my $othervar2 = $_[4];
... do stuff ...
}

# call it
report(\%hash1, \%hash2, \%hash3, $othervar1, $othervar2);
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