It's a shame the teamid is a subtag and not an attribute, you will be unable to use the "start" rules. Which will make the script a bit slower, but not more memory hungry. In this case I think

my $parser = XML::Rules->new(
 rules => [
  _default => 'content',
  user => sub {
   return unless $_[1]->{teamid} = $_[4]->{parameters}{teamid};

   delete $_[1]->{_content}; # delete the textual context (whitespace)
   return '@user' => $_[1];
  },
  users => 'pass no content',
 ]
);

my $users = $parser->parsefile( $the_xml_file, {teamid => 100};
[download]

should give you the data for the right users only.