In the last 15 years, in the National League, there have been 16 playoff teams that have outperformed their Pythagorean W-L record by 5 or more wins. This number includes 3 teams from the 2011 season who have already outpaced their number by 5 wins, or on pace to (Atlanta 4, Milwaukee 6, Arizona 5). Of those 16 teams, only 3 times has that outperformance, or good luck, been the difference between a playoff spot and golf in October.
The 1998 Chicago Cubs had a 90-73 record, claimed the Wild Card spot with a game 163 win over the San Francisco Giants, but a Pythagorean W-L record of 85-72. If not for the good luck, the Giants most likely would have won the Wild Card outright.
The 2001 Houston Astros had a 93-69 record, but a Pythagorean W-L record of 88-74. Had it not been for the good luck, the Chicago Cubs would probably have gotten the Wild Card that year, with the Cardinals slipping up to division champions. The Cubs had a Pythagorean W-L that year of 89-73.
But the luckiest post season appearance belongs to the 2007 Arizona Diamondbacks, who went 90-73, claimed the NL West title on a tie breaker with the Padres and Rockies. That year, the D'Backs outperformed their Pythagorean W-L record by an incredible 11 wins. Had it not been for this good luck, the Padres and Rockies most likely would have not had to play a game 163, the Padres would have been the Wild Card winner, and Tony Gwynn Jr.'s walk off triple scoring Corey Hart against the Brewers off of Trevor Hoffman wouldn't still be aching Padre fans.
Of the 10 other instances of outperforming (not including the 3 possible for this year) playoff teams above their Pythagorean W-L record by more than 5 wins, mentioned above, none of them resulted in being a difference maker for that playoff spot.
The 2003 San Francisco Giants beat their Pythagorean W-L record by 7 wins, but they won the NL West that year by 15 games over the Los Angeles Dodgers.
The 2011 Milwaukee Brewers are poised to be the benefactors of some historic luck in their playoff race in the NL Central. The team is on pace to outperform their Pythagorean W-L record by 8 wins. They currently sit at 73-51 outperforming the Pythagorean W-L record by 6 wins to date. Their closest competitors in the division, the St. Louis Cardinals, apart from key injuries to Adam Wainwright, and a bevy of key players spending considerable time on the DL, have had a tiny bit of bad luck as far as Pythagorean W-L, but sit exactly at the same number as the Milwaukee Brewers, at 67 wins.
Before yesterday's 5-1 loss to the possible NL Cy Young winner, Clayton Kershaw, the Brewers were on a torrid 19-2 run in their last 21 games. This stretch of games is the thing that has valuted them from being a half game out of first place to being 7 up today on the Cardinals.
During a stretch like that, no matter who the team is, or how bad or good the team is or its competition, there will be some luck involved. No team can maintain a .905 winning percentage.But a team has to be a "good" team as well to keep winning, even if you throw in some luck here or there.
So are the Brewers really good, or just really lucky?
During that stretch of games, the Brewers played series against the Astros twice, the Cardinals twice, the Cubs, the Pirates and the Dodgers. Adding up the W-L records of those teams and weighting number of games versus the various opponents comes to an opponent combined winning percantage of .437. If you play a team with a .437 winning percantage 21 times, you should expect to go 12-9 against them, the Brewers went 19-2. So there is somethign to be said here that the level of competition the Brewers have faced during this stretch, has been fortunate, but also lucky to he tune of about 7 wins. And the scheduling luck for the Brewers will continue to the end of the season. They only have 3 series left against teams that currently have a winning record (Phillies and 2 against the Cardinals).
During this stretch of games, the Brewers have outscored their bad opponents 97 to 48, which would translate into a Pythagorean W-L record fo 17-4. So that probably accounts for some of the luck you might expect from a team on such a hot streak.
But if you look even deeper at some of the peripherals, the Brewers were even really lucky there. During the past 30 days, their vaunted offense has been a middle of the pack performer, with a BABIP of .317 which isnt really lucky, but isnt really unlucky either. The pitching is where a ton of the luck has come from. During the past 30 days, according to fangraphs, the Brewer pitching staff has a .249 BABIP surrendered and an xFIP of 3.44 vs their actual ERA of 2.25. Both the starters and relievers have had an ERA - xFIP of around 1.60 or so, again lucky. And the relievers have a BABIP against of .240. This would great luck would probably help account for a lot of the 1 run games they have won during the stretch (3-1 in one run games; 4-0 in 2 run games; and 1-1 in 3 run games). It is very beneficial, if during 50% of your games you have a very lucky pitching staff to bail out your average offense.
I believe that this years Milwaukee Brewers are a good team. I predicted they would win 88 games and just barely miss the playoffs, but I dont know if anyone could have predicted how lucky this team was going to be. Statistics tells us that at some point that luck is bound to run out. Hopefully for Brewer fans that time doesnt come until November.
Update: After sweeping the Mets this weekend, the Brewers have now gone 22-3 over their last 25 games. Their Actual W-L record is now 7 wins above their Pythagorean W-L record, and despite the fact that they are 8 1/2 games up on the Cardinals, the Cardinals have the exact same Pythagorean W-L record. The pitching staff BABIP is .259, third best in baseball and the best among playoff contenders, and their ERA-xFIP is a whopping 1.04 runs per game, which is nearly a third of a run luckier than the next closest rank.