I love this site and have learned more about PERL here, than any other website

Not much, I guess ;^). Please, it's "Perl" (mind the capitalization).

@look = <INF>;

It's better to use <DATA> for your code. That way, the data goes with the program and you don't have to provide it separately.

@out = sort { (split '|', $a, 12)[4] <=> (split '|', $b, 12)[4] } @look;

You need to quote the pipe: '\|'.

@fields = @$line;

$line is not an arrayref. The split you did only extracted the 4th field of the string for sorting, nothing more. @out is a regular array of strings, like @look.

Applying this comments, and adding strict and warnings, your code becomes:

my @look = <DATA>;
my @out = sort { (split '\|', $a, 12)[4] <=> (split '\|', $b, 12)[4] }
+ @look;
foreach my $line (@out) { 
    print $line;
}
__DATA__
accred|143|0|0|412|0|0|0|0|0|0|0|0|
accu-b|36|0|0|103|0|38|0|0|0|0|2|0|
accua|35|0|0|27|0|37|0|0|0|0|1|0|
[...]
[download]

If you want to access the fields individually, you have to perform another split inside the foreach loop.

Further on, doing a Guttman-Rosler transform, it could be:

## tested
my @out =
    map { substr $_, 6 }   ## hardcoded "6" here...
    sort
    map { my $val = (split /\|/)[4]; sprintf "%06d$_",$val }  ## ... a
+nd here
    <DATA>;
[download]

my @d = <DATA>; my @e; my @key = map { (split /\|/)[4] } @d;
use Benchmark qw/cmpthese/;
cmpthese (4e4, {
    grt    => sub { @e = map { substr $_, 6 } sort map { my $val = (sp
+lit /\|/)[4]; sprintf "%06d$_",$val} @d; },
    raw    => sub { @e = sort { (split '\|', $a, 12)[4] <=> (split '\|
+', $b, 12)[4] } @d; },
    ambrus => sub { @e = @d[ sort { $key[$a] <=> $key[$b] } 0 .. @d - 
+1 ]; },
});
[download]

          Rate    raw    grt ambrus
raw     2742/s     --   -58%   -92%
grt     6547/s   139%     --   -80%
ambrus 33058/s  1106%   405%     --
[download]

Update: Added benchmark. || Included ambrus' solution.