Breaking down Masahiro Tanaka’s strong second half for the Yankees

The first half of 2017 was not a good time to be a Masahiro Tanaka fan. Beginning with the very first day of the season, in which Tanaka pitched an absolute stinker against the Tampa Bay Rays, it seemed like every fifth day brought a new low for Tanaka. However, he improved markedly in the second half, posting a 3.77 ERA and pitching gems in all of his postseason starts.

About a month ago, I argued that Tanaka was poised for a similar second-half performance in 2018 as well. I noted that Tanaka’s mediocre first half wasn’t the result of a decline in ability, as he wasn’t allowing hard contact on the daily. His strong core skills - a sparkling strikeout rate backed up by his extremely effective secondary pitches, coupled with an above-average ability to limit walks - were also still intact. My argument was that Tanaka’s results were marred by an abnormally high home run rate, and that all he needed was better luck on his fly balls in order to improve.

So far in the second half, that’s exactly what has happened for Tanaka. Despite coming off a tough loss against the White Sox in his most recent start, Tanaka currently owns a second half ERA of 2.89, backed up by a FIP of 3.34. What’s more, he’s done that not by altering his pitch mix or location, but by remaining, at least to the untrained eye, the same pitcher as he always was. What’s changed is his luck on fly balls, which has taken a significant turn for the better.

First, let me show you some graphs visualizing how Tanaka’s approach hasn’t changed. Here’s a line graph showing how Tanaka’s pitch usage has changed over the course of the 2018 season, from BrooksBaseball.net.

Pitch mix wise, nothing much has changed for Tanaka between the first and second half. His basic approach of pitching backwards - that is, eschewing his four-seam fastball and throwing his splitter and slider early on in the count - has remained the same. Therefore, it’s impossible to attribute Tanaka’s first half struggles, or his second half surge, on his pitch usage.

Some of you might think that better location is the answer, which is certainly a sensible guess. However, this isn’t the case with Tanaka. Here are the heatmaps for Tanaka’s pitch count by location in the first half, for left-handed hitters:

And right-handed hitters:

Looking at these heatmaps, it’s easy to ascertain Tanaka’s attack plan in the first half - keep the ball low and away. Call it Pitching 101, sure, but if you were a pitcher with Tanaka’s control/command skills and breaking stuff, you’d probably do the same. Has Tanaka changed his approach in the second half? Judging from his second half heatmaps, the answer appears to be a resounding “no”.

So, we’ve established that second half Tanaka looks a whole lot like first half Tanaka, in that his pitch usage and location is basically the same. Yet his results - a 4.54 ERA prior to the All-Star break, compared to a 2.89 ERA after, just to give you a reminder - have been night and day. The difference for Tanaka, it appears, hasn’t been improvement in skill or approach, but in luck on fly balls.

Luck on fly balls is captured well by a stat called Home Run to Fly Ball rate, or HR/FB. True to its name, it represents the ratio of home runs given up for each every fly ball that a pitcher allows. It’s also a very fluky stat with very little predictive power from year to year, because pitchers don’t have much control over whether the deep fly balls that they allow end up on the warning track or in the front row bleachers.

HR/FB perfectly captures how Tanaka’s fortunes have turned regarding the fly balls that he gives up. In the first half of 2018, Tanaka’s HR/FB was 20.9%, an astronomical figure. In other words, on average, one in every five fly balls that Tanaka gave up from March to early July ended up beyond the fence. However, in the second half, Tanaka has enjoyed a much lower HR/FB of 14.7%, or something like one dinger for every seven fly ball allowed. Accordingly, Tanaka’s HR/9 has decreased between the All-Star break from 1.94 to 1.03, which has done wonders for his run prevention numbers.

So, Tanaka’s second half surge has been driven not by adjustments in approach, but by better luck on fly balls. This may sound disappointing at first, as you’d normally hope improvements to be backed up by skill rather than luck. However, it’s not like Tanaka’s getting lucky per se; it’s more accurate to say that Tanaka was suffering from rotten luck in the first half, and now his luck is more or less normal, allowing his strong strikeout and walk numbers to shine through. The saying goes, it’s better to be lucky than good, but so far in the second half, Tanaka has been both luckier and good.