December 30th, 2019

xBA on Fastballs vs. Offspeed Pitches, Part 1

​As a fantasy community, we love talking about xStats. I decided to take a fresh approach in analyzing xStats and what that may mean for 2020. One thing that has not been analyzed enough in the industry is the difference between xBA (expected batting average) on the three types of pitches: fastballs, offspeed, and breaking ball pitches. If I'm a major league front office (I'm not), I would imagine that it would be easy to identify which hitters fare well (or should fare well) on certain types of pitches, and that certain hitters are seeing too much of those pitches (and vice versa). If a player fares well on fastballs relative to the other types of pitches, and sees a ton of fastballs (55%+), we should assume with reasonable certainty that he will see less of those pitches the next year. ​

Francisco Mejia hits changeups better than fastballs, and should be expected to see more fastballs as a result.

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​To analyze the graph above, let's start with the most glaring example, Ian Happ. Happ had a paltry xBA of .189, .176 lower than his xBA on offspeed pitches. He crushes offspeed pitches relative to fastballs. This also applies to 2018 (.080 better on offspeed pitches). So, we know a trend is forming with Happ. Given that he is seeing 49% fastballs already, there isn't much room for him to go up. A deeper dive shows that Happ hits 36% of fastballs he puts into play to the opposite field, and another 36% to straightaway center. Simply put, he is habitually late on fastballs. If I'm the rest of the league, I'm upping that percentage to 55%, until he can prove that he can handle fastballs. Given that we know this data, we shouldn't expect the Player of the Week from the last week of September to be all that relevant in fantasy.

On a similar end, we have Francisco Mejia, who crushes offspeed pitches. But, he is only seeing 40% fastballs! We know that number is going to increase next year, and if he starts getting hyped up based on his prospect pedigree, you'll know better. Make him prove that he can hit fastballs before diving in. 

Conversely, we have the opposite - guys who smack around fastballs, but have trouble with the change:

Joey Gallo has a league-average xBA on fastballs, and is significantly worse hitting offspeed pitches.

​Judging by this graph, it is crazy that someone would throw Starling Marte a fastball 59% of the time. I would expect the league to adjust, and throw less fastballs going forward. Now, Marte is a veteran with an above-average track record, and is rightfully taken within the top 60 picks on an annual basis. However, looking at a younger guy like Rhys Hoskins with less of a track record, we are led to believe that he should be thrown less fastballs and more secondary pitches. Given that he is currently going ahead of Eloy JImenez in 2020 mock drafts, this type of analysis should shine light on the fact that he is overrated. You'll know better than to draft Hoskins at his ADP (or at all - I'm still salty that I took him in the fifth round in The Great Fantasy Baseball Invitational). 

I plan to expand this analysis to breaking balls and xSLG as the offseason progresses. Let me know your questions and any particular players you are interested in!