Heyward has some really weird batted ball data. To cut to the chase, he's always been a HEAVY pull hitter at 42.1%. League overall excluding pitchers averaged 40.7% in 2018. The reason this is weird is his 2019 spray rates look like this 26.3%/49.5%/24.2% for pull/center/oppo. For more context, the least pull hitter in 2018 was Mauer at 25.5%. What we've seen through a pretty decent sample size here is Heyward go from a pretty pull heavy hitter to among the least pull heavy in the majors. He currently leads the majors in lowest pull rate.
What's interesting to me anyways is that from my understanding the reason you sell out that much as a pull hitter typically is to get to your power. But in Heyward's case this year hitting the ball to center and oppo more in fact arguably has made his power better. His hard hit rate has fallen some since his scorching start but it's more or less within his normal range. However his medium contact rate is up(5%) and almost all of that coming from his soft contact rate going down. His .200 ISO is the second highest in his career behind only 2012 where hit 27 HRs.
When you add in the fact his walk rate is 14.0%... I really don't think any of this is smoke and mirrors. One could argue this is literally the best hitter Heyward has ever been. Normally you'd look at his rookie year for that. But consider this, his walk rate in 2010 was 14.6% to 14%, his k rate was 20.5% to 14.7%, his iso was .179 to .200 this year, and he hit .277/.393/.456 that year to his current .267/.371/.467 but remember that he also had a .335 BABIP in 2010 to his current BABIP is .274.
What's also interesting to me is I feel like people sorta view Heyward on the down side of his career just because he's already been a FA but he's only 29 this year. That's typically when most players hit FA. So, seeing him actually become better isn't that crazy. Jose Bautista had 0.4 career fWAR from 23-28. His age 29 year he broke out for 6.6 fWAR followed by 8.1, 3.1 in about 2/3 of a season, 4.1, 6.2, and 5.2 before he finally fell off the rails at 35. There's numerous other examples of guys busting out at 28-29.
