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New Vegas & game time features on Team Game Finder

Posted by Mike on November 2, 2012

Spending a lazy Friday morning at work? No fear, we've put a couple of new features up on the Team Game Finder tool.

First off is the addition of Vegas betting lines (from 1978 to now) to the additional search criteria selector, with which you can find games in the past 5 years in which a team was favored by more than 10 points or 17+ point underdogs in the last 30 years. We also have Over/Under lines, with which you can find all Patriots games since 2002 with an O/U greater than 50.

Next, we've added game time and time zone selectors to the filter criteria, with which you can find that the Bengals have a .700 record since 2002 in games played at 4pm in the Eastern time zone or that the Green Bay Packers have the best record in the last 15 years in road games on the West Coast.

1 Comment | Posted in Features, Pro-Football-Reference.com

Estimating NFL Win Probabilities for Matchups Between Teams of Various Records

Posted by Neil on October 30, 2012

WARNING: Math post.

PFR user Brad emailed over the weekend with an interesting question:

"Wondering if you've ever tracked or how it would be possible to find records vs. records statistics....for instance a 3-4 team vs. a 5-2 team...which record wins how often? but for every record matchup in every week."

That's a cool concept, and one that I could answer historically with a query when I get the time. But in the meantime, here's what I believe is a valid way to estimate that probability...

  1. Add eleven games of .500 ball to the team's current record (at any point in the season). So if a team is 3-4, their "true" wpct talent is (3 + 5.5) / (7 + 11) = .472. If their opponent is 5-2, it would be (5 + 5.5) / (7 + 11) = .583.
  2. Use the following equation to estimate the probability of Team A beating Team B at a neutral site:

    p(Team A Win) = Team A true_win% *(1 - Team B true_win%)/(Team A true_win% * (1 - Team B true_win%) + (1 - Team A true_win%) * Team B true_win%)

  3. You can even factor in home-field advantage like so:

    p(Team A Win) = ((Team A true_win%) * (1 - Team B true_win%) * HFA)/((Team A true_win%) * (1 - Team B true_win%) * HFA +(1 - Team A true_win%) * (Team B true_win%) * (1 - HFA))

    In the NFL, home teams win roughly 57% of the time, so HFA = 0.57.

This means in Brad's hypothetical matchup of a 5-2 team vs. a 3-4 team, we would expect the 5-2 team to win .583 *(1 - .472)/(.583 * (1 - .472) + (1 - .583) * .472) = 61% of the time at a neutral site.

Really Technical Stuff:

Now, you may be wondering where I came up with the "add 11 games of .500 ball" part. That comes from this Tangotiger post about true talent levels for sports leagues.

Since the NFL expanded to 32 teams in 2002, the yearly standard deviation of team winning percentage is, on average, 0.195. This means var(observed) = 0.195^2 = 0.038. The random standard deviation of NFL records in a 16-game season would be sqrt(0.5*0.5/16) = 0.125, meaning var(random) = 0.125^2 = 0.016.

var(true) = var(observed) - var(random), so in this case var(true) = 0.038 - 0.016 = 0.022. The square root of 0.022 is 0.15, so 0.15 is stdev(true), the standard deviation of true winning percentage talent in the current NFL.

Armed with that number, we can calculate the number of games a season would need to contain in order for var(true) to equal var(random) using:

0.25/stdev(true)^2

In the NFL, that number is 11 (more accurately, it's 11.1583, but it's easier to just use 11). So when you want to regress an NFL team's W-L record to the mean, at any point during the season, take eleven games of .500 ball (5.5-5.5), and add them to the actual record. This will give you the best estimate of the team's "true" winning percentage talent going forward.

That's why you use the "true" wpct number to plug into Bill James' log5 formula (see step 2 above), instead of the teams' actual winning percentages. Even a 16-0 team doesn't have a 100% probability of winning going forward -- instead, their expected true wpct talent is something like (16 + 5.5) / (16 + 11) = .796.

(For more info, see this post, and for a proof of this method, read what Phil Birnbaum wrote in 2011.)

3 Comments | Posted in Announcement, Pro-Football-Reference.com, Stat Questions

Incomplete Stats for 10/29

Posted by Mike on October 30, 2012

Due to hurricane-related issues with our data provider, stats for the Monday night NFL game are incomplete. We will update them as soon as we have the data, but until that point the player pages for 49ers and Cardinals players will be missing yesterday's game stats.

Comments Off | Posted in Announcement, expire7d, Pro-Football-Reference.com

Support Pro-Football-Reference.com, Sponsor a Page

Posted by Neil on October 29, 2012

Sponsoring a page is fun, fast, and easy way to support what we're doing here at Pro-Football-Reference. With a sponsorship, you can:

  • Show your support for your favorite player or team.
  • Drum up traffic for your own site & draw in fans with a common interest.
  • Get some well-deserved recognition for your support of PFR.
  • Make your voice heard by the tens of thousands of people who visit Pro-Football-Reference every day.

Here's all you have to do to get involved:

  1. Create a membership account.
  2. Find the page(s) you'd like to support, and click "sponsor" (available pages).
  3. If the page you want is already sponsored, click "Alert Me!" to be informed when the current sponsorship expires.
  4. Follow the instructions to create your message and make your payment.
  5. Your message and links will be visible on the page after we approve them (usually in less than 24 hours).

And who knows, if you're clever enough, your message might end up on lists like these.

Comments Off | Posted in Announcement, Pro-Football-Reference.com, Sponsors

PI Player Game Finder

Posted by Neil on October 28, 2012

Comments Off | Posted in Announcement, Play Index, Pro-Football-Reference.com

ESPN’s Total QBR Added to Player Pages and Leaderboards

Posted by Neil on October 12, 2012

Just wanted to let everyone know that we have now added ESPN's Total Quarterback Rating (QBR) to our player pages and leaderboards.

In case you forgot what QBR is all about, here's a link describing the methodology behind the rating (they also noted several subsequent tweaks here). The scale is 0-100, with average being 50; the best performers tend to be around 75-80 for a full season (Aaron Rodgers set the record with 86.2 last year), while something like the 11.7 that JaMarcus Russell put up in 2009 would be considered the bottom of the barrel.

7 Comments | Posted in Advanced Stats, Announcement, Pro-Football-Reference.com

CFB Updates

Posted by Neil on October 4, 2012

A quick note about several updates that we added to SR/College Football this week:

Comments Off | Posted in Announcement, CFB at Sports Reference, Features, Pro-Football-Reference.com

NFL Records After N Games, Part II

Posted by Neil on October 3, 2012

I posted this a few weeks ago, to answer the basic question of "When an NFL team starts the season with a given record, what winning percentage do they tend to end the season with?":

Longtime S-R friend Carl Bialik of the Wall Street Journal asked to see those numbers broken out by the frequency of each final record, so I thought I'd put that together for today:

Comments Off | Posted in Announcement, Data, Pro-Football-Reference.com

NFL Officials Pages

Posted by Mike on September 27, 2012

As you might have noticed, NFL officials have been in the news a bit lately. Because of this, we've just put up NFL officials pages from 2000 through the current season, featuring everyone from the most popular man in Green Bay to a certain workout enthusiast. On each page you'll find season totals which include a breakdown of how his crews tended to call games vs. league averages and below that, complete game logs dating back through the 2000 season.

2 Comments | Posted in Announcement, Features, Pro-Football-Reference.com, Uncategorized

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