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Joe Mauer has been a very good two-strike hitter over the past three seasons, slashing .243/.309/.344. His .653 OPS with two-strikes is 17th highest in baseball, and his 220 hits are the fifth highest total in that timeframe (minimum 750 plate appearances).

Mauer's successful hitting with two-strikes can be attributed to how he handles inside pitches, both in and out of the strike zone. Of his 220 two-strike hits, Mauer has 67 (30%) of them on pitches over the inside part of the plate (see chart to the right). Overall he's hit .345/.368/.495 (.862 OPS) on two-strike inside pitches he put in play, with 10 doubles, two triples, and five home runs.

The data suggests that Mauer changes his approach on inside pitches depending on the strike count. With less than two strikes, Mauer appears to show a greater willingness to wait on these pitches and drive the ball to the opposite field. Only 59% percent of his hits are pulled to the right side of the field on inside pitches with less than two strikes. With two strikes, Mauer pulls 84% of inside pitches. It seems like he is more willing to get the bat head out in front and drive the ball, knowing that he can't let the pitch beat him inside.

Data Sources: BaseballSavant.mlb.com, Baseball-Reference.com

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Eddie Rosario is a free-swinger. In 2015 and 2016 combined, he had a 3.3% walk rate that ranked third lowest in the majors and a 0.13 walk to strikeout ratio that was the lowest in baseball (minimum 800 PA's). One particular area of the strike zone that tempted Rosario's free-swinging ways was pitches up-and-in, out of the strike zone. Rosario swung and missed at these pitches 24.2% of the time in 2015-16. That was, by far, the highest swing and miss rate by any left-handed hitter on pitches in this part of the zone (see chart to the right). It was a full 11 percentage points higher than Rougned Odor, who had the second highest rate at 13.2%.

That changed in 2017. Rosario still swung at a lot of pitches up-and-in, out of the strike zone (his swing rate on these pitches actually went up in 2017 to 69% from 62%in 2015-16), but he missed on those pitches significantly less. As mentioned above, Rosario swung and missed at 24.2% of those pitches in '15-16, but that dropped to 16.3% in 2017 (see second chart to the right). Not only was he making more contact in 2017, he also made better contact. In '15-16, Rosario had two extra-base hits on these pitches. In 2017, he had 10 extra-base hits on up-and-in pitches (the most in baseball), including five home runs.

The question is: What does this means for Rosario's 2018 season? He's still a free-swinger that offered at even more pitches out of the zone in 2017. Yes, he made more contact and had pretty good success, but continuing to swing at bad pitches is rarely a sustainable path to long term success.

Data Sources: BaseballSavant.mlb.com, FanGraphs.com

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When the Twins signed Jason Castro to a three-year, $24.5 million contract prior to the 2017 season, they were doing so with the expectation that he would continue his defensive status as one of the top pitch framers in baseball. Based on the pitch framing data compiled by StatCorner.com, Castro was the seventh-best framer in the majors in 2015 and the fifth-best in 2016 by Runs Above Average (RAA). His RAA in those years was 12.9 and 12.8, respectively. That translated into a net addition of 97 called strikes in 2015 and 96 called strikes in 2016.

But 2017 was a different story. Castro finished with an RAA of -9.7, ranking 29th of 42 catchers that caught a minimum of 4,000 pitches. That resulted in a net loss of 73 called strikes for Twins pitchers. So what happened?

One area where Castro's pitch framing declined significantly was on borderline pitches on his glove side. The chart to the right shows the yearly called strike percentage on borderline pitches that Castro caught on his glove (left) side. In both 2015 and 2016, roughly 74% of borderline pitches Castro caught on his glove side were called strikes. That dipped down to 62% in 2017. To put that in terms of called strikes, if Castro had converted the 454 pitches he caught on his glove side at a 74% rate instead of a 62% rate, Twins pitchers would've had an additional 54 called strikes.

The full 12 percentage point drop from 74% to 62% doesn't fall solely on Castro's shoulders. Of the borderline pitches Castro caught on his glove-side in 2015 and 2016 combined, Statcast had 51% of them falling in the strike zone. In 2017, Statcast had only 48% of those borderline pitches as strikes. So three percentage-points of that 12 percentage-point drop can be explained away. But that still leaves a nine percentage-point difference that's attributable to some skill decline from Castro. 

Data Sources: BaseballSavant.mlb.com, StatCorner.com

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In the three seasons from 2015 through 2017, Brian Dozier has hit 104 home runs, the tenth highest total in baseball during that time-span. Much of that production has come in the upper two-thirds of the strike zone and on pitches up-and-out of the strike zone (see the zone chart to the right). In total, 82 of Dozier's 104 home runs (79%) have been hit off of pitches located in the upper two-thirds of the strike zone. Another 16 (15%) were hit on pitches up-and-out of the strike zone. Only six (6%) were hit on low pitches, with five of them being on pitches in the lower-third of the strike zone.

Based upon those stats, it seems obvious that pitchers should locate the ball low in the strike zone and below the strike zone to Dozier as much as possible. So why are only 36% of the pitches he's faced over the past three seasons located there? The reason appears to be that it's difficult for pitchers to get a called strike against Dozier on pitches low in the strike zone.

Take a look at the second strike zone chart to the left. Pitches that Dozier doesn't swing at in the upper two-thirds of the strike zone are called correctly 95.1% of the time. However, called strike accuracy against Dozier on pitches located in the bottom third of the strike zone is much lower. Over the past three seasons combined, only 42.9% of pitches in the bottom-third have correctly been called strikes against Dozier. The rate was even lower than that in 2017, with only 39.2% accuracy.

If 42.9% seems like a very low rate of accuracy, it is. The graph below shows that, over the past three seasons,  Brian Dozier has the lowest called strike rate against on pitches in the bottom-third of the strike zone in all of baseball. And frankly, it's not even close. There's a 15.9 percentage point gap between Dozier and Robinson Chirinos, who has the second lowest called strike accuracy rate against in baseball (58.8%). Dozier has benefited from incorrect calls low in the zone more than any other player in baseball.

Whether or not Dozier is conscious of the less accurate (essentially smaller) strike zone he's given, it's likely a significant help to him. When pitchers aren't getting calls in the lower third, they're forced to come up in the zone. That should allow Dozier to focus on a much smaller strike zone that, as it happens, is the portion of the zone where he crushes baseballs.

Data Sources: BaseballSavant.mlb.com and Baseball-Reference.com