Here's a kinda fun solution. Can you see how it works?

use warnings;
use strict;

my $flips = 'TTHHHHTHHHHHHTHT';
my $flops = substr $flips, 1;
my ($maxT, $maxH, $side) = (0, 0, substr $flops, 0, 1);
my $toggles = ($flips ^ $flops);

$toggles =~ tr/\0\x1c/01/;
my @runs = $toggles =~ /(0*1)/g;

for my $run (@runs)
  {
  $maxT = length $run if $side eq 'T' && length $run > $maxT;
  $maxH = length $run if $side eq 'H' && length $run > $maxH;
  $side = $side eq 'T' ? 'H' : 'T';
  }

print "Longest heads run is $maxH\n";
print "Longest tails run is $maxT\n";
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Prints:

Longest heads run is 6
Longest tails run is 2
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