by Jim Glass
Vince Lombardi's post-season coaching W-L record of 9-1, .900, is the best ever. Or maybe not, some say Joe Gibb's record of 17-7 is standard to beat - "only" .708, but over a run of 2.4 times as many games it is much harder to keep a big winning record. How can we compare them?
One way is to compute the binomial probability of a coach attaining a given won-loss record by random chance. For instance, in Herm Edwards' first year coaching my Jets, he went 10-6. I was happy. That .625 winning record was better than Tom Landry's .607 and our former coach Bill Parcells' .570 - better than a Hall of Famer's and sure future Hall of Famer's! It looked like we had a great coach. Except that Parcells earned his .570 over 303 games and Landry earned his .607 over 418, while Herm had earned his .625 over only 16.
The binomial calculation can give the probability of winning a given number of games out of any number played, and so providea a common standard to apply to the W-L performances of different coaches with different W-L percentages over differing numbers of games. It told me that, assuming game outcomes were random with a 50% chance of winning/losing, Herm's record of .625 (or better) had only a 22% probability of occurring by random chance, which was pretty encouraging - but Bill's .570 record had only a 1% chance, and Tom's .607 had only a 0.001% chance. So perhaps it was premature to declare Herm a better coach than Tuna and Tom (as indeed it turned out to be).
Now it's playoff time, so I wondered: what if we applied this common standard when looking at the playoff coaching records of Belichick, McCarthy, Dungy, and all the other coaches of all post-season games back to 1950? And suppose we set the random probability of winning each playoff game not at 50%, but at the actual probability of winning indicated by the relative strength of the competing teams and home field advantage?
Which coaches would we see to have beaten the odds, which not, and who would the surprises be? This is the exercise followed below.
I used the PFR.com data base to compile a list of all NFL post-season games and coaches from 1950 through 2010, using teams' "Simple Rating System" numbers to gauge their relative strength. The SRS gives a team's strength-of-schedule adjusted average net points per game (points for minus points against) compared to the league average. To this I added 2.5 points to the rating of the home team (when there was one). From the resulting point differential the conventional Pythagorean formula provides a winning probability for each team in each game.
Taking all the games for each coach, the resulting "Unit Pythagorean" rating provides his expected W-L percentage.
Using this percentage instead of 50% as the probability of winning, the binomial calculation gives the probability of the coach's actual W-L record resulting from random chance.
Take Dick Vermeil as an example. His 6-5 winning record with a Super Bowl championship appears very credible on its face. But his teams averaged a full touchdown better than the opposition by SRS, were the higher rated in every single game, and on top of that had home field advantage seven times to only twice for the opponent. All this gives him a .689 expecting winning rate, the highest of any coach with three or more post-season games. Put that into the calculator and it says his actual 6-5, .545 record was better than only a meager 9% of those expected by chance - random chance would beat his playoff record 91% of the time.
At the other extreme, Blanton Collier as the successor to the great Paul Brown disappointed the Browns fans of his day by going only 3-4 in the post-season. But as he had only a .255 expected winning percentage, his .429 winning record was superior to .746 of those expected by chance, the highest binomial rating of any coach with a losing record.
More recently, Ken Whisenhunt has gone 4-2, .667, in the playoffs with only a .281 expected winning rate, giving him a winning record better than .944 of those expected by chance - the highest binomial rating among all the 128 coaches to take a team to the playoffs since 1950. (Lombardi is #2.)
The numbers, and interpreting them
I've limited the list below to the 70 coaches who have coached five or more playoff games since 1950.
Given for each is the number of playoff games coached, his W-L count, actual winning percentage, expected winning percentage, and the binomial calculation of the percentage of random results his record exceeds. Thus, a figure of .612 indicates the coach's record is better than 61.2% of the records produced by chance (given his expected winning percentage).
Personally, I do not consider these numbers to be very persuasive evidence of "how good" a coach is or was. The sample sizes for all are small to very small and vary greatly, and random results in just a few close games can make a very big difference in the binomial result.
But this data does show, objectively, how well each coach's actual record in the playoffs compares to reasonable expectation. Is Coach X's "great" record in the playoffs really as good as it looks? Is Coach Y's "poor" record actually better than it looks? Does Marty Schottenheimer really have the worst playoff coaching record of all time? (No, but close.)
For perspective on (and arguments about) such questions, I think this data is useful.
|Rank||Name||Games||Won||Lost||Won Lost%||Expected WL%||Binomial Performance||1||Ken Whisenhunt||6||4||2||0.667||0.281||0.944|
|70||Jim Mora, Sr.||6||0||6||0.000||0.597||0.000|