Searching For The Source Of Fernando Tatis Jr's May Struggles

At the end of April, we were discussing Fernando Tatis Jr. in the context of a return to superstardom and as a fixture in the National League MVP race. As we prepare to hit the end of May, we've watched Tatis Jr's offensive performance sink with the majority of the rest of the San Diego Padres offense. 

Tatis' March & April included a slash of .345/.409/.632 to go along with a .257 isolated power, and a strikeout rate of just 15.0 percent. His wRC+ sat at 182. Add in the baserunning prowess (seven steals) and the defense and you had a player looking every bit like his old self again.

But May has been far from the same story. He's hitting only .195 and reaching base at a mere .267 clip. The power has dwindled to a .195 ISO while his cumulative performance has resulted in a wRC+ of just 83. What is perhaps most notable is that his walk rate — which sat a shade over 10 percent in March & April — has dwindled to just 7.8 in May. This, while his strikeout rate has shot up to 26.7 percent.

The strikeout rate would appear to be the source of what has held Tatis Jr back during his May swoon. If you can't put the ball in play, you can't deploy your 93rd percentile Hard-Hit% (53.6 percent). Except assuming that he's simply striking out more and, thus, not hitting would represent an oversimplification. 

Such an oversimplification implies that Tatis is swinging more or chasing more. Except he isn't. In fact, Tatis' plate discipline numbers should bely a player experiencing a similar level of success that we saw in the previous month. His 49.5 Swing% and 30.9 Chase% in March & April each went down in May (47.0 Swing%, 29.2 Chase%). Notably, his swing rate inside of the zone fell most among the plate discipline figures. After hacking at pitches in the zone roughly 77 percent of the time at April's end, he's swinging at such pitches 73.8 percent of the time. It's not a drastic change, but it is the second-most significant among the trends in his approach. 

The most significant is in his zone contact. Tatis Jr has made contact inside the zone just 83.2 percent of the time this month; he was at 89.5 in March & April. It's there we might find some semblance of a reason for his struggles this month. That reasoning exists almost exclusively due to offspeed pitches. 

Opposing pitchers haven't changed much in how they navigate a Fernando Tatis Jr. plate appearance this year. They're coming into the zone roughly as much while the distribution of pitch types has changed only marginally. What is worth paying attention to, though, is the bringing of offspeed pitches into the strike zone: 

That's about a 12 percent increase on off-speed pitches inside the zone. Tatis has experienced trouble with that pitch type this year, whiffing at it 46.9 percent of the time. For context, breaking pitches are in second at just 32.0 percent. So it's possible that an adjustment is needed against that pitch type in particular in order to get Tatis back on track.

It's also important to note that the off-speed stuff doesn't represent the entirety of a source. There's a luck component, as his BABIP is at just .222 after a .356 start to the year. That will even out and help him to compensate on its own. 

The good news here is that there isn't anything severe plaguing Fernando Tatis Jr.at the plate. It's not an expansion of the zone or a general context issue. Nor is it a zone swing issue, as he's largely focused on the same areas that he did to start the year. Pitchers have simply adjusted in the way they pitch to Tatis. Now he has to adjust back.