my $in_combat = 0;
#open the file for input
LINE:
while (my $line=readline($input_file)) {
   if (# line contains start-combat flag) {
      $in_combat = 1;
   }
   next LINE if (!$in_combat);
   # do stuff with lines *during* combat--beginning and end will be here, too!
   if (#line contains end-combat flag) {
      $in_combat = 0;
   }
}
# close files, etcetc