How good is the Astros 2019 pitching staff, really? Is it better than the 2018 edition?

One of the best baseball writers of our time, Mike Petriello, wrote an intriguing article about the Astros pitching staff published by MLB.com. In This staff could be Majors’ most dominant ever, Petriello uncovered this rather amazing statistical nugget; that the Astros staff in 2019 has the lowest on base percentage in history.

While acknowledging the greatness of the 2018 Astros staff, Petriello suggested, despite the losses the staff underwent in the off-season, that perhaps the 2019 staff is even better. This based on the following criterion, that with a historic, all-time low, .274 OBP against, the Astros staff does the most basic job of a pitching staff— preventing “runners from reaching base.”

It is a fascinating article, which makes many interesting and unexpected statistical connections. I wish I had written it, but then, that’s why he’s there, and I’m here.

Nonetheless, the article brings up two questions: 1. Is the Astros 2019 staff the most dominant ever and 2. Is it better than the 2018 staff?

Start with #1.

Petriello’s conclusion is not true in part because his premise is false. The basic job of pitchers is not to keep runners from reaching base, that is only a means to the end. The basic job of pitchers is to prevent runs.

Indeed, the Astros in 2019 are elite in preventing base runners. They have the second lowest WHIP in history, just behind the 2019 Dodgers, and just ahead of the 2018 Astros. But wait, the top three in WHIP were all in the last two years. And eight of the top twenty all came since 2015. Is this a modern trend and, if so, does that negate the historic significance of low OBP and WHIP numbers?

To a degree, yes. This is the era of lift and launch, when strikeouts outnumber hits, but home runs are being hit league wide in record numbers. In the last few years run-scoring strategy has evolved towards lower on base percentages and higher slugging percentages, especially from home runs. The Astros lead in low OBP is just the leading edge of a trend throughout baseball, but it does not signify pitching dominance.

For 2018-19, SLG PCT league wide is at a near all-time high, at .426 both years, eighth all-time. But OBP is closer to the lowest all-time, .318 in 2018, and .321 for 2019, ranked 88th and 81st respectively since 1920.

Yet, these very low OBP’s have not resulted in very low run production. League wide run production in 2018 was 16th highest all-time. The league record for home runs was set in 2017, and 2018 saw the fourth most homers in league history. Having a low OBP is futile if a large proportion of the people who are getting on base are circling the base paths with their hits.

Although endowed with a historically low OBP, the 2019 Astros SLG PCT at .387 is 263rd best since 1920. Number 3 ranked in OBP, the 2018 Astros had a .358 SLG PCT, 151st in history. This same team allowed 1919 Total Bases, 140th in league history (not including 2019 teams) and 152 home runs, 248th in league history. And the 2019 staff is even more prone to the home run ball, allowing 1.4 per nine innings, compared to 0.9 for the 2018 staff.

So, to say that the Astros staff may be the most dominant in history because it doesn’t allow many base runners, but then ignore that the same staff gives up one more home run for every two games than its immediate predecessor, is misleading. The 2019 staff gives up more bases, and gives up more runs, 3.11 ERA for the 2018 Astros, to 3.55 ERA for the 2019 Stros.

There is also the issue of adjusting for eras and ballparks. Luckily, Baseball Reference included it’s adjusted ERA statistic, ERA+ in this year’s Play Index feature. This compares a team’s ERA to other teams that same year, and a number higher than 100 indicates a team is that much better percentage-wise than league average.

So how are the 2019 Astros by ERA+? Their 124 means the Astros are twenty four percent better than league average. That ranks 34th best in Major League history, not bad at all. You might even call that dominant. But not nearly as much so as the 2019 Tampa Bay Rays at 145, best all time so far. However, peripheral stats predict significant regression from the Rays.

Question #2

Which leads us to the second question. Which staff is better, the 2018 Astros or the 2019 Astros? We’ve already pretty much covered this, but a few more points.

By ERA+, the 2018 Astros at 133 are tied for seventh best all-time with the 2016 Cubs. This year’s Astros are at 124. The top team all-time, this year’s Rays, is in a wait and see status as almost two thirds of the season remains. Two of the teams ahead of the 2018 Astros are WWII era Cardinals teams, and WWII era teams aren’t realistic comparisons. Surprisingly to me, the 2018 Astros staff outperformed the 1972 Orioles, the 1997 Braves and the 1966 Dodgers, among a number of other iconic staffs.

So I believe you can reasonably say the 2018 Astros staff was fourth or fifth best in history. Although it trails the 2019 Astros by microscopic amounts in terms of WHIP and OBP, it had more SO/9 (10.4-10.0) and more SO/W. (3.88-3.63) Most significantly, the 2018 Astros had a lower SLG PCT, allowed .5 fewer home runs per nine innings, and, as already stated, allowed about a half run less per game.

Billy Beane supposedly said “that the only thing that matters is on base percentage.” I actually don’t believe for a second he ever said anything so asinine. If baseball games were decided by which team got the most base runners, then the 2019 Astros would be the most dominant pitching staff in history because it is the best at preventing base runners. But because doubles and home runs are more damaging than singles and walks, and because they do more to lead to what does decide games, i.e. runs, the Astros 2018 staff’s elite run prevention leaves it unchallenged as the best Astros staff ever, and one of the best in the history of baseball.