Just based off pure win-loss records, if I asked you which teams have been the best in 2018, I would think the Yankees and Red Sox would be the first two teams to pop into your head. If I asked you to name some of the best teams ever, I’m sure the usual suspects, such as the 1927 Yankees, 1975 Reds, 1998 Yankees, and the 2001 Mariners would come to mind. I’m also fairly sure most of the general consensus wouldn’t put any of these 2018 teams in the same room as those historically great teams.

Now what if I told you there was in fact a historically great team playing in the current progression of this 2018 season, and that they weren’t even leading their respective league in winning percentage, let alone currently ranking third in that department.

But this so happens to be true. The best team in baseball so far this year hasn’t been the Yankees and it hasn’t been the Red Sox. It’s the Astros, and they might be the best team in the history of modern baseball.

Now that my overly-dramatic intro is finished, let’s get down to business. The Astros are good (bold, I know right). Everyone knows this. In the time of when this was written, they own a 12-game winning streak and sit atop the AL West by two games.

With that out of the way, this brings up the fair question of why would a team that is currently the third best team in the major leagues in terms of winning percentage be considered an all-time great team? Well to start, the remarkable start by the pitching staff is no secret. As it stands, their starting rotation would have the highest K% in MLB history and their bullpen would have the second highest mark in history (only behind the 2018 Yankees). The offense is no issue too, pacing to lead the majors in wRC+. All these tidbits help the argument, but the main reason for this opinion lies in the great world of run differential, or pythagorean winning percentage to a deeper level.

To get right to it, no team in the history of modern baseball (I’m going back to 1960 for this study), has ever finished the season with a higher per game run differential greater than two. The highest ever was the 1998 Yankees, sitting at +1.907. The 2018 Astros are currently sitting at +2.139, so there is definitely a fair chance they could achieve this.

Breaking that per game run differential into a scaled measurement of pythagorean winning percentage, the Astros come out as having an expected winning percentage of 72.2%. This tops all major league teams easily, with the Cubs coming in next at 65.4%. The Astros separation between their pythagorean winning percentage and actual winning percentage of 65.3% also leads the majors. Let’s see how that pythagorean record compares with some of the great teams of the modern-era.

Top 20 Pythagorean Winning Percentages (1960-) Season Team W L Actual WP% Pythag. WP% Season Team W L Actual WP% Pythag. WP% 2018 Astros 47 25 65.28% 72.19% 1969 Orioles 109 53 67.28% 67.74% 2001 Mariners 116 46 71.60% 66.99% 1998 Yankees 114 48 70.37% 66.79% 2016 Cubs 103 58 63.98% 66.30% 2017 Indians 102 60 62.96% 66.22% 1975 Reds 108 54 66.67% 65.74% 1974 Dodgers 102 60 62.96% 65.43% 2018 Cubs 40 27 59.70% 65.41% 1998 Braves 106 56 65.43% 65.40% 1998 Astros 102 60 62.96% 65.06% 1971 Orioles 101 57 63.92% 64.77% 2018 Red Sox 48 24 66.67% 64.54% 2018 Yankees 46 20 69.70% 64.40% 1995 Indians 100 44 69.44% 64.29% 1976 Phillies 101 61 62.35% 64.25% 1970 Orioles 108 54 66.67% 64.17% 1993 Braves 104 58 64.20% 63.94% 2001 Athletics 102 60 62.96% 63.89% 1968 Tigers 103 59 63.58% 63.68%

It goes without saying that the Astros would totally be fine playing under the level of their pythagorean winning percentage all year, pacing for a 106-56 record at the moment (pace of their pythagorean record is 117-45). But we can probably expect some forward progression in the second half of this season. This development comes as bad news to the Mariners. With the Astros only leading the AL West by a mere 1.5 games, it would seem as if they would have more than a fighting chance at the division with more than half the season left. But, if the Astros start pulling closer to their expected record, they’ll have no chance. It’s also worth noting while the Astros are performing at a historical level, the Mariners are over-performing at a historical pace.

Largest pythagorean winning percentage over-performances (1960-) Season Team W L Actual WP% Pythag. WP% Differential Season Team W L Actual WP% Pythag. WP% Differential 2018 Mariners 46 25 64.79% 54.24% 10.54% 1981 Reds 66 42 61.11% 52.40% 8.71% 2016 Rangers 95 67 58.64% 50.48% 8.17% 2004 Yankees 101 61 62.35% 54.71% 7.63% 2008 Angels 100 62 61.73% 54.20% 7.53% 1972 Mets 83 73 53.21% 45.92% 7.29% 1984 Mets 90 72 55.56% 48.36% 7.19% 1970 Reds 102 60 62.96% 55.82% 7.14% 2017 Padres 71 91 43.83% 36.71% 7.11% 1981 Orioles 59 46 56.19% 49.16% 7.03% 2012 Orioles 93 69 57.41% 50.45% 6.96% 2007 Diamondbacks 90 72 55.56% 48.75% 6.81% 2005 Diamondbacks 77 85 47.53% 40.74% 6.79% 1961 Reds 93 61 60.39% 53.78% 6.61% 1994 Pirates 53 61 46.49% 40.22% 6.27% 1997 Giants 90 72 55.56% 49.48% 6.07% 2009 Mariners 85 77 52.47% 46.47% 6.00% 1977 Orioles 97 64 60.25% 54.35% 5.90% 1978 Reds 92 69 57.14% 51.42% 5.72% 2016 Phillies 71 91 43.83% 38.18% 5.64%

It’s hard to improve the following season after a World Series win. Most teams actually start a decline. But the Astros are doing just the opposite of that. They’re getting better. Significantly better. And their improvement might just lead them to becoming one of the greater teams in the history of modern baseball.

*All graphs are as of June 17th