Perl Pigskins Picks

[Anonymous Monk]

I've always been a nut about predicting NFL games. Since I was a kid I've been working this system on paper. Well not for the last couple of year.

System is this. Each team has an offense and defense power rating. Say the Niners have OFF=44 and DEF=27 and the Giants have OFF=40 and DEF=20. Each teams predicted score is just its OFF - opponents DEF. The home team gets a 3 point bonus. So:

Niners = 44 - 20 = 24
Giants = 40 - 27 + 3 = 16

Niners only scored 16 so their OFF gets adjusted down and Giants DEF gets adjusted up by (24 - 16) / 7 = 1.1428.

Giants only scored 13 so their OFF goes down, Niners DEF goes up by (16 - 13) / 7 = .4285

7 is just a fudge factor to keep ratings from changing too fast because of upsets. 3 home field points is also fudge. After trying many values, it seemed these gave the best result. That was a while ago, maybe they should be checked again.

PickemFoo

Season beginnings are always tricky but based on two years of scores, my picks:

FortyNiners 16 (24)   Giants      13 (16)
Jets        00 (22)   Bills       00 (18)
Ravens      00 (24)   Panthers    00 (12)
Vikings     00 (12)   Bears       00 (26)
Chargers    00 (14)   Bengals     00 (18)
Chiefs      00 (22)   Browns      00 (21)
Falcons     00 (15)   Packers     00 (30)
Colts       00 (24)   Jaguars     00 (31)
Lions       00 (12)   Dolphins    00 (23)
Eagles      00 (28)   Titans      00 (19)
Cardinals   00 (14)   Redskins    00 (21)
Rams        00 (30)   Broncos     00 (18)
Seahawks    00 (19)   Raiders     00 (23)
Saints      00 (16)   Buccaneers  00 (32)
Cowboys     00 (15)   Texans      00 (23)
Steelers    00 (16)   Patriots    00 (19)

#!/usr/bin/perl

   use strict;

   my $SCORES = 'scores.txt';

   # Format of scores file is:
   #    visitors score hometeam score
   #    one score per line
   #    for games not yet played, scores are 0
   #    Like: Patriots 20 Rams 17

   my $OFF    = 42;           # Default offense rating
   my $DEF    = 21;           # Default defense rating
   my $HOME   = 3;            # Home field advantage
   my $ADJUST = 7;            # Adjustment factor

   my (%nfl, $wins, $loss, $length);

   if (!open (IN, $SCORES)) {
      printf STDERR "\nError opening file: $SCORES\n$!\n\n"; exit;
   }

   while (chomp (my $line = <IN>)) {

      if ($line =~ m{__END__}) { last; }
      if ($line =~ m{^\s*$})   { next; }
      if ($line =~ m{^\s*#})   { print "$line\n"; next; }

      if ($line =~ m{(\S.*\S)\s+(\d+)\s+(\S.*\S)\s+(\d+)}) {

         my ($away, $anum, $home, $hnum) = ($1, $2, $3, $4);

         if (!defined($nfl{$away})) {
            $nfl{$away} = { off => $OFF, def => $DEF};
            if (length($away) > $length) { $length = length($away); }
         }

         if (!defined($nfl{$home})) {
            $nfl{$home} = { off => $OFF, def => $DEF};
            if (length($home) > $length) { $length = length($home); }
         }

         my $atry = int($nfl{$away}->{off} - $nfl{$home}->{def});
         my $htry = int($nfl{$home}->{off} - $nfl{$away}->{def} + $HOM
+E);

         if ($atry == $htry) { $htry++; }

         my ($actual, $guess, $result);

         if ($anum != 0 || $hnum != 0) {
            $actual = $hnum - $anum;
            $guess  = $htry - $atry;

            if ($actual * $guess > 0) { $wins++; $result = '++'; }
            else                      { $loss++; $result = '  '; }

            adjust($nfl{$away}, $nfl{$home}, $anum, $atry);
            adjust($nfl{$home}, $nfl{$away}, $hnum, $htry);
         }

         printf (STDOUT "%-*.*s %2.2d (%2.2d)   \n",
            $length, $length, $away, $anum, $atry);

         printf (STDOUT "%-*.*s %2.2d (%2.2d)   ",
            $length, $length, $home, $hnum, $htry);

         printf (STDOUT "%+2.2d (%+2.2d) %s\n\n",
            $actual, $guess, $result);

      }
      else { print STDERR "Unknown format:$line\n"; }
   }

   for my $team (sort { $b->[0] <=> $a->[0] }
                    map { [ $nfl{$_}->{off} + $nfl{$_}->{def},  $_]; }
                       keys(%nfl)) {

      $team = $team->[1];

      printf(STDOUT "%-*.*s %4.1f %4.1f %4.1f\n",
         $length, $length, $team,
         $nfl{$team}->{off} + $nfl{$team}->{def},
         $nfl{$team}->{off}, $nfl{$team}->{def})
   }

   printf (STDOUT "\nW:$wins L:$loss %5.2f%\n",
      ($wins / ($wins + $loss)) * 100);

#-----------------------------------------------------------
sub adjust {

   my ($team, $oppo, $score, $guess) = @_;

   my $adjust = ($score - $guess) / $ADJUST;

   $team->{off} += $adjust;
   $oppo->{def} -= $adjust;
}

[YuckFoo]

Uh-oh, wasn't logged in.

LogFoo

[/dev/trash]

I'm not sure I understand....what exactly is scores.txt? Does it need to get updated every week?

[YuckFoo]

I was leaving it as an exercise for the programmer to LWP over to nfl.com and pickup the scores, but here is a scores file for 2001 and the first weeks of 2002 anyway. Yes, it should be updated weekly. Supply a week of 0 - 0 scores to get a prediction.

The code only called 6 of 15 games correctly yesterday but averages about 64% correct over the past couple of years. I'm not sure the NFL can be predicted a lot better. Here's a data set if anyone wants to come up with a better recipie.

ScoreFoo

Read more... (11 kB)

[/dev/trash]

Oh okay. That makes sense. I think I'll enjoy this one.