Astros Observations: Time to delve into on-base percentage!

ARLINGTON, TX - JUNE 07: Alex Bregman #2 of the Houston Astros scores a run in the fourth inning against the Texas Rangers at Globe Life Park in Arlington on June 7, 2018 in Arlington, Texas. (Photo by Ronald Martinez/Getty Images)
ARLINGTON, TX - JUNE 07: Alex Bregman #2 of the Houston Astros scores a run in the fourth inning against the Texas Rangers at Globe Life Park in Arlington on June 7, 2018 in Arlington, Texas. (Photo by Ronald Martinez/Getty Images) /

Since the Astros’ 2018 season is now roughly 39.5% finished, let’s compare data from this year to the 2017 championship campaign.

Thanks to a certain book by author Michael Lewis and a certain movie that starred actor Brad Pitt, on-base percentage has gained quite a bit of notoriety among most baseball fans. Unlike other famous novelties portrayed in cinema, on-base percentage is still an important metric in evaluating a baseball player’s performance. On-base percentage can be defined simply as not making an out. In baseball, if you’re a hitter, not making an out is the best thing you can possibly do. Teams only have 27 of those in a nine-inning game, so outs are a scarce resource.

Now, the 2017 Astros have long been established to have been a terrific offense. If you will, an historic offense. One reason why last season’s lineup was so dang good was their ability to get on-base. In 2017, the Astros’ offense finished with a .346 on-base percentage, the best in baseball. The next closest teams were the Indians and Yankees with a .339 on-base percentage. The same amount of separation — .007 or 0.7% — between the Astros and second place was the same between  separation second and ninth place.

Like I said, the Astros in 2017 had a terrific offense. The best in baseball by far.

Fast forward to the 2018 Astros and the offense is still quite good. A .329 on-base percentage through the team’s first 64 games of the season. Fifth-best in baseball entering Friday, June 8th. Not too shabby. But the offense has not replicated the success they had last year despite most of the lineup remaining in place from their championship squad. Regression has been the primary culprit as multiple players like Marwin Gonzalez and Yuli Gurriel. Even Jose Altuve, the 2017 AL MVP, has regressed. This regression is reflected across various metrics, like on-base percentage.

On-Base Percentage Difference (2017 vs. 2018)

Out of the gate, we notice that Jake Marisnick has experienced the sharpest decline in on-base percentage. Although this development is rather disappointing, it is of no terrible surprise since Marisnick’s lack of getting on-base has been often highlighted. In 120 plate appearances this season, Marisnick has only walked three times and struck out 56 times. It is quite easy to see why his on-base percentage has decreased by 14.3%. The next highest is Derek Fisher’s 8.5% drop in on-base percentage followed by Gonzalez at 7%.

Out of the 14 players I compared, only four showed a positive change in their respective on-base percentage.

Only one, though, has more than 117 plate appearances this season: Alex Bregman with 277 plate appearances. While Max Stassi, J.D. Davis, and Tony Kemp have demonstrated improvement, each have do not have the extended track record against major league pitchers to draw concrete conclusions. But the trends do indicate that they have improved based on their playing time last year at the major league level, which has been comparable to the 2018 sample size.

Ironically, the Astros’ walk rate as a team — 8.8% — has increased by 0.7% based on last year’s total of 8.1%. But the strikeout rate has risen by 4.5% when you compare 2017 and 2018 data. The increase in strikeouts from one season to the next would at least partially explain the drop in on-base percentage.

Regarding hits, the Astros averaged 9.76 hits per game if you take the hit total from 2017 (1,581) and divide it by the numbers of games played (162). When you you use the same calculation for this year’s data (562 divided by 64), the hit total per game drops to 8.78 hits per game. The Astros have essentially averaged one less hit per game this season compared to their 2017 counterparts. A rather elementary equation, sure, but it does provide a quick snapshot of another potential reason behind the team’s drop in on-base percentage. And less hits equals a lower on-base percentage.

Next: Astros in the Minors: Forrest Whitley to start on Friday

Without delving into too much more data, the Astros this season have walked more but their strikeout rate increase has overshadowed the gain. In combination with fewer hits when compared to last season’s average and you can begin to see why the Astros have a lower on-base percentage in 2018. And the lower on-base percentage has been one reason behind the still-good, but less-than-historic offense of the Astros. Since this season’s data is still incomplete by nearly 60%, these figures can easily change. But at this point, the trends are starting to become difficult to ignore.

**Statistics and information courtesy of FanGraphs**