Two nights ago, Miami Marlins starting pitcher Wei-Yin Chen struck out 12 batters in 6 1/3 innings en route to a tight 3-2 victory over the Milwaukee Brewers. He looked fantastic in the start and he is working on bringing his early ERA difficulties to a close in Miami. The $80 million man and owner of the biggest pitching contract the Marlins have ever handed out has started out the season awkwardly with a 4.40 ERA. However, his FIP is down at 3.55 and his defense-independent ERA predictors like xFIP and SIERA have him playing at a level of around a 3.70 ERA. Chen so far has allowed the lowest rate of home runs in his career but is otherwise looking very similar to his successful 2015 version in terms of strikeouts and walks.
Chen was previously known as a "FIP beater" in the sense that his career defense-independent numbers have always been worse than his ERA. This year, the trend is confusingly reversed without much explanation. He is allowing a higher average on balls in play, as hitters are batting .329 against him when they keep the ball in the park. That should improve naturally as the season progresses, but it should be noted that it does not come without a reason. The exit velocity on Chen's pitches is up from 87.6 mph last season to 89.9 mph this year, a jump of more than two mph.
Now, this may mean nothing, especially if a pitcher's approach has not changed. But oddly enough, after spending years pitching in a similar fashion, a lot of the batted ball results for Chen are pointing to some significant changes. He has upped his ground ball rate to 45 percent from a career rate around 39 percent. He also has lost one of his biggest weapons early this year in the pop-up; after 2.3 percent of all pitches last season ended up in a pop-up out for Chen, this year that rate has dropped down to 0.8 percent.
You can clearly see why this might be happening based on the early difference in heat maps in terms of Chen's location. Take a look at his fastballs from 2014 to 2015.
In this heat map, you can see that Chen primarily worked in the strike zone and inside versus right-handed hitters. He also split his work more evenly lower and higher in the zone, and in particular he threw a decent number of pitches in that upper inside corner. This was discussed when he signed with the Marlins as one reason why Chen's ERA and run-suppression has surpassed the expectations of defense-independent stats like FIP. A solid additional two percent of all pitches, 60 additional batted balls last season, essentially turned into strikeout-equivalents or automatic outs!
This year, things are really different.
That cannot be a coincidence. The Marlins are notorious for getting their pitchers to throw low in the strike zone and pitch to weaker contact. Chen, a pitcher who induces weak contact via his own approach, comes to Miami. Within seven starts, he is throwing lower in the strike zone than he has since he has gotten to the United States. Not only is Chen tossing a solid 16.3 percent of his pitches in the lower parts of the zone as compared to 14.8 percent of his pitches in the previous two years, but he is also seemingly abandoning the upper half of the zone. This year, Chen has only thrown 7.9 percent of pitches high in the zone and only 6.3 percent in that upper-in or upper-mid part that he used before to get popups. That is down from 12.4 percent and 8.7 percent respectively from 2014 to 2015.
Again, this seems more intentional rather than coincidental. The Marlins like their pitchers to throw low in the strike zone and suddenly a guy who signs with them immediately changes his heatmap in that direction? This may be amenable to a pitcher who struggled badly with home runs in the past and needed an overhaul, but Chen was mostly a finished product when he arrived in Miami. The team may have thought that throwing low in the zone may reduce his known home run issue, and indeed he is allowing a smaller number of home runs. However, this may have happened simply because of a change in home venues, with Marlins Park being a homer-suppressing stadium as compared to Camden Yards. The Marlins may have gotten that decrease in home runs without tinkering with Chen's gameplan.
This move has had unexpected consequences. The loss in pop-ups is real. If Chen allows a similar number of batted balls in play, going from 2.3 percent of pitches resulting in automatic outs to 0.8 percent of pitches is a real difference. Even a drop of two percent to one percent over 3000 pitches a season results in a nearly 13-run difference over the course of a full season! Allowing an extra 13 runs in a full year is probably worth a little more than one win lost in an entire year. Even more conservative estimates put the loss in popups at about an eight-run loss in a season.
Of course, some of that is offset by gaining ground balls, which are less valuable to hitters. If you can turn a few outfield fly balls into ground balls, there is definite value in avoiding home runs. However, that difference may be a smaller one. Going from a ground ball rate of 40 percent to one of 44 percent, even assuming all of those would-be fly balls would have been more valuable regular flies rather than popups, would only be worth almost four runs.
Overall, you are looking at at least shaving half a win off of Chen's performance potentially by moving to this new approach based on the early results. Of course, Chen could adjust to pitching in this new style and get better at it; after all, pitchers adjust quickly, and Chen has been good at getting weaker contact than usual before. But with this radical move, the question becomes whether Chen and the Marlins tried to fix something that simply was not broken.