During Yu Darvish’s first eight starts, he faced eight different teams, making his first regular season start against each of them. His last four starts, however, have been repeat performances, as he’s faced the Mariners, Angels, Blue Jays, and Athletics for the second time. During those four starts, he’s been awful.

May 21st, @ SEA: 4 IP, 5 H, 4 R, 6 BB, 5 K

May 27th, vs TOR: 5 IP, 7 H, 3 R, 3 BB, 3 K

June 2nd, @LAA: 6.1 IP, 6 H, 3 R, 3 BB, 7 K

June 7th, @Oak: 5.1 IP, 6 H, 6 R, 6 BB, 4 K

You don’t need to know much about statistical analysis to know that 18 walks in 20 2/3 innings pitched is not good, and any pitcher issuing that many free passes probably isn’t going to be successful. But, is the recent failure to throw strikes related to opposing batters learning how to approach Darvish after getting an earlier look at him?

That appears to be a fairly popular theory at the moment, but let’s look and see whether the evidence supports the idea. Let’s start with the plate discipline stats, which seem like the most likely place where a change in batter approach would be the most noticeable.

In his first eight starts, 46% of the pitches Darvish threw were defined as being in the strike zone according to PITCHF/x. Opposing batters swung at 43.2% of these pitches and made contact on 74.4% pitches that they swung at. All of these marks were a bit below the league average, but not extremely far from what the norm.

So, what about in these last four starts? Darvish has actually thrown a higher rate of pitches that PITCHF/x thinks have been strikes (48.3%), but opposing batters have kept their bats on the shoulders more often. The swing rate against Darvish since May 21st is just 40.1%, with the decline coming both on pitches in and out of the zone. Three of the four teams swung the bat less often in their second match-up against Darvish than they did in their first.

SEA: 41.8% Swing% on 4/18, 39.6% on 5/21

TOR: 45.4% Swing% on 4/30, 42.4% on 5/27

LAA: 41.9% Swing% on 5/11, 44.1% on 6/2

OAK: 44.9% Swing% on 5/16, 34.6% on 6/7

Patience has never really been the Angels thing, and it’s probably not a coincidence that his start against Anaheim is also the only one of the last four where Darvish has actually performed decently. The A’s, Blue Jays, and Mariners were all content to let Darvish pitch himself into trouble, and he responded by doing just that.

However, we can’t ignore the fact that PITCHF/x thinks Darvish’s rate of throwing strikes has actually gone up lately. In fact, his starts against Settle and Toronto at the end of May are his only two starts all year where the system believes that more than half of his pitchers were in the strike zone, and yet, he issued nine walks and only had eight strikeouts in those two starts. What do we make of that?

Maybe the batters aren’t the only ones adjusting to Darvish’s reputation for poor command. Take a look at this strike zone plot from TexasLeaguers.com for those two games against the Mariners and Blue Jays:

There are 16 pitches within the boundaries of the strike zone as defined by PITCHF/x that were called balls and exactly one pitch that is outside the defined borders that was called a strike. The starters for the Mariners (Felix Hernandez) and Blue Jays (Kyle Drabek) combined to have seven pitches within the PITCHF/x strike zone called balls in those same games with those same umpires, and they got three pitches out of the zone as called strikes.

This isn’t to say that umpires are definitely squeezing Yu Darvish. PITCHF/x has a margin for error, and most of the pitches that were called balls are close enough to the edge that they could have legitimately been low or outside. And, of course, the umpires had nothing to do with Darvish’s disaster start yesterday, where nearly 40% of the pitches he threw were outside the strike zone. However, there is some evidence to suggest that Darvish hasn’t been getting some calls lately, and just as the league has picked up on his command problems and is swinging the bat less, it is also possible that umpires are less likely to give Darvish the benefit of the doubt on marginal pitches that could go either way.

As Patrick Kilgo noted in his presentation at the SABR convention last year, there is some evidence that umpires favor veteran players when it comes to calling balls and strikes, and better pitchers get more calls than others. It’s a widely held belief in the game that guys who are consistently around the zone get the benefit of the doubt on borderline calls, and Darvish is certainly not a guy who can paint the corners with consistency.

So, are big league hitters adjusting to Darvish? It does look like they’re trending towards swinging less often, which makes sense considering his command problems. However, they’re not the only ones who seem to be adjusting to Darvish, and he’s going to have to be aware of the fact that he’s probably a bit less likely to get calls on the corners until he establishes himself as a guy who can throw strikes with regularity.

The batter/pitcher match-up is a game of constant adjustment. If opposing batters are going to make Darvish throw strikes, he’ll need to adjust and be more aggressive in getting getting ahead in the count. The best way to get hitters to chase pitches out of the zone is to put them in defensive counts, and if they’re going to take a more passive approach at the plate against him, he has an opportunity to throw first pitch strikes and start hitters off 0-1 until they adjust.

Darvish has Major League stuff – and despite his recent struggles, his command doesn’t appear to be getting worse – but Major League hitters aren’t going to keep getting themselves out if he doesn’t start giving them a reason to. Whether it’s a mechanical adjustment or simply a decision to actually use the entire plate (right now, he just doesn’t throw inside against left-handers), Darvish is going to have to make some changes in order to counter the reputation that he garnered in his first two months in the big leagues. Good stuff and bad command is a better place to start from than vice versa, but if Darvish is going to become the guy he was billed as, he’s going to have to attack the strike zone in a way that he hasn’t so far.