Where have Masahiro Tanaka's strikeouts gone?

Although strikeouts aren't everything to a pitcher, piling up Ks is often a hallmark of dominance. This isn't to say a starting pitcher can't be among the best in baseball without gaudy strikeout totals, but it's always a bit disappointing and worrisome when a player stops putting batters away like he used to.

A player that has gone through that downward trend is Masahiro Tanaka. Yes, he's been one of the best pitchers in baseball this season, and his 2.91 ERA and other numbers leave no doubt that he is an ace for the Yankees. But, he has regressed in one area since debuting with the Yankees in 2014: strikeouts. In his rookie year, Tanaka sported a 9.31 K/9. It dropped down to 8.12 last season, and has all but bottomed out at 6.60 this year. He hasn't seen other numbers affected by this deterioration, but the downward trend is concerning and worth looking into.

A quick look at PITCHf/x whiff numbers should provide the answer to where Masahiro Tanaka's strikeouts went. Unfortunately, not much clarity comes upon first viewing.

Data via Brooks Baseball

There are no clear trends that suggest a huge downward swing in strikeouts from his whiffs per swing mark. Still, there are two initial takeaways from the data: he's really getting more whiffs on the fastball and really losing whiffs on the splitter. Besides that, there's not a whole lot to see on the surface. But, there's more to this story.

An interesting part of Tanaka's season is that he has all but cut out the fourseam fastball from his repertoire. That ‘gain' you see in whiffs from the fastball is negligible, since he's thrown it all of 37 times this season. Interestingly, Tanaka has swapped out the heater with a sinker, which has gone from the fourth most used pitch in his arsenal to the most used.

This move is a good one for Tanaka, as the sinker is much better than the fourseamer when to reducing hard contacting and increasing ground ball rate (which has helped his GB% increase by 5.3% this season). Unfortunately, it's a trade off because the sinker isn't going to get swings and misses like his fourseamer did.

Probably the most striking part of that chart is the splitter's whiff per swing rate crashing. In 2014, the only pitches that got more swings and misses than Tanaka's splitter were Yusmeiro Petit's curveball, Ervin Santana's slider, and Stephen Strasburg's changeup. This season, there are seven pitchers whose splitters get more whiffs than Tanaka's does. The pitch is still just as hard to drive as it was in 2014, but the swing and miss qualities have evaporated. The velocity remains, but the pitch has lost some drop. I don't think that's really the primary cause, though.

Instead, it may have to do with where he throws the splitter. If you have a splitter like Tanaka does, burying it below the zone is going to get whiffs. This season, Tanaka has elevated the pitch slightly more, sneaking it into the strike zone on occasion. A side effect of this approach could be strikeouts. This isn't easy to see when looking at a heat map of both right handed and left handed hitters, but becomes more apparent with righties.

Brooks Baseball

Coincidentally, the splitter's whiff rate hasn't fallen against left handed hitters from 2015 to 2016, only right-handed batters. For the first time, there's a noticeable platoon split with whiffs from the splitter, and it happens to come at the same time that he's using the pitch differently based on handedness.

We've talked about how the strikeouts could be dropping because of what pitches Tanaka is throwing and where he's throwing these pitches, but how about when he is throwing these pitches? On two strikes, it would make sense to lean toward using the best pitch for whiffs more often. That would mean relying on the splitter and slider. Tanaka follows that line of thinking with the slider, but has really cut down on throwing the splitter with two strikes. Prior to this season, the splitter was thrown 43% of the time against lefties and 36% of the time against righties with two strikes. In 2016, he's cut those rates down to 38% (not a big difference) and 22% (a pretty big difference) against left handed and right handed hitters, respectively.

When a pitcher stops striking hitters out, it can be concerning because it often means a decrease in skill level. If the pitches aren't as nasty, hitters won't miss as much. What follows often isn't pretty. Luckily, that doesn't seem to fully be the case with Tanaka.

The righty has swapped the fourseam fastball for the sinker, which is a tradeoff as the sinker is a better pitch overall, but doesn't cause as many whiffs. The splitter has lost its special ability to cause swings and misses, and this could be a sign of the pitch simply losing some effectivity. At the same time, it's just as tough to hit well, so it's nothing to sound alarms over. Instead, the lack of whiffs could be due to location. On a related note, Tanaka seems to be choosing to veer away from the splitter with two strikes. I don't really see why this would benefit him, but it could explain the decrease in strikeouts overall. Some of these changes are understandable tradeoffs, and others could just be flukes that will correct themselves over the season. Either way, there's no reason to be overly worried about Tanaka for now.