Have you ever heard the phrase, “Man, hitter X is really locked in at the plate”? Sure you have, but that’s a bit of a vague statement. What does it mean to be locked in at the plate? People often use this cliché and just leave it there. From people who are around the game, when this phrase is dropped, it gives off a sense of “well you’re just supposed to know what I mean.”

Does it mean you just submitted your final answer to a game show and are awaiting to see if you got it right? Does it mean you’re chained to the plate, and you can only be freed by finding the key to the batter’s box? Maybe it means a hitter signed a really bad cellphone contract and now they can’t change services. Any of these things could be possible, but if you’re looking for a more reasonable answer: locked in is what Bryce Harper has been over the first four weeks of the season.

But don’t take my word for it; other people are noticing it, too. Here is Matt Wieters about a week ago:

"It's fun to watch when one of the best players in the game is locked in," catcher Matt Wieters said.

And Dusty Baker after an opening day homerun:

“He was a guy that was locked in first in spring training,” Nationals Manager Dusty Baker said.

Still, we haven’t gotten to the root of the issue. What does it mean to be “locked in” at the plate? Harper is, of course, hitting like a monster, running a triple slash of .432/.548/.824, with seven home runs and more walks (19) than strikeouts (14), good for a wRC+ of 252 and a WAR of 2.1, both of which lead the league. But being locked in is about more than just stats or outcomes; it’s about the way that the Nationals wünderkind has reached this incredible level of offense. For Harper, and many others, this means that a hitter is being selective at the plate. It means that they are seeing the ball so well that they aren’t getting fooled or beat by a “pitcher’s pitch.”

I like to visualize this as a hitter watching an 0-1 slider running away from them that lands maybe three inches off the outer black, because they recognize that it’s both a ball and a pitch that they couldn’t do much with anyway. This isn’t the only example, but consistently taking close pitches is a testament to a hitter’s patience and pitch recognition. Taking pitches that might be strikes but aren’t in your “happy zone” as a hitter? Well, that’s the next step above patience. That comes from an understanding of who you are as a hitter and what portions of the zone you have the most success in. The converse is when a hitter recognizes and capitalizes on mistake pitches that are left in said “happy zones.” That combination of patience and self-awareness is what makes for, in my mind, the state of play that we call “being locked in.”

In Harper this year, both qualities aren’t hard to see. The young left-hander has displayed more patience than we have ever seen from him before. Especially this early in the year, where other stats may be lacking, plate discipline statistics carry a lot of information. For Harper, these stats tell a real story about his development, a story about how he is treating pitches in the strike-zone:

It’s clear that Harper has dialed back the amount he swings little by little. In fact, he has swung around four percent less every individual year since 2014—a gradual drop that reflects a desire and ability to be more selective. Harper has developed from a guy who broke into the bigs as an eager free-swinger, swinging well above the league average rate at pitches in the strike zone, to a hitter now well below the league average rate for strike zone swings. The story was about the same for his contact rates in the strike zone, only inverse—low Z-Contact rates until a steady improvement following the 2014 season has put him well above league average.

It shouldn’t be understated how directly this points to Harper being more selective and successful at the plate. Having a selective approach is one thing; actually implementing and capitalizing on that strategy is another.

It isn’t as if Harper is swinging much less overall—the difference compared to last season is about a percentage point—and he’s chasing pitches outside the strike zone at about the same rate. And if you think Harper is seeing less pitches in the strike zone, meaning he can take more pitches without having to worry about being behind in counts, well do I have news for you. The youngster is seeing more pitches in the zone this season (47 percent) than he ever has in his career, with the previous high coming in 2014, when he saw 45 percent of his pitches fall within the strike zone. It should come as no surprise that Harper is averaging just over four pitches every plate appearance.

Pitchers are attacking Harper, and he is… letting them attack him. Harper has learned that patience, even on pitches inside the strike zone, will net him the pitch he is looking for. But where exactly is this majestic pitch he is looking for?

Back in 2015 Harper had an interview with Eno Sarris of FanGraphs, in which he said this:

“Of course I’m pulling for power but I want the ball to left center, and I enjoy pitches on the outer part of the plate,” continued Harper. “Joey Votto talked to me four or five years ago, said if you want to hit .300 and you want to do what you want to do, you have to hit the ball to left field.” (…) Here’s the thing about using this knowledge about Harper’s preference for pitches on the outside part of the plate: it’s not easy. Even as Harper admits that executing his strategy of going the other way can be tough — “It’s getting harder every single year, because you’re seeing guys that are better. You’re seeing guys that are out of the pen at 98 mph and you’re seeing lefties that are 97, 98 also and can spot it” — it’s even harder to take advantage of his lone weakness. So, try to throw the ball inside to Bryce Harper. If you do it once, are you going to go there again? “If you can pick a guy out of the big leagues that can throw three straight heaters on the inside part of the plate, and paint those pitches, I’ll tip my cap to them,” said Harper. “If they can do that, that’s very impressive.” So far, they haven’t been able to. The player will still have his approach — “You just wait for that pitch out over and try not to swing at the pitch inside half” — but he’s not too worried about it. “You’re not going to find that guy that can paint on the inside half.”

There’s a lot of juicy content in that one quote. Harper looks for a ball out over the plate, and tries not to offer at pitches in the inner half. Opting for outside pitches as opposed to inside pitches has been a staple of Harper’s approach so far, but one he took a bit too far in 2016. This season, Harper has reaped the benefits from letting pitches near the outer black go by. Be they a strike or a ball, just as Harper said, he can wait the pitcher out to get a better pitch. This is just what we have seen this season:

Because Harper isn’t offering at pitches outside of his zone as much as he has in the past—his swing rates have fallen the most on the outside portion of the plate, in the strike zone but not Harper’s “happy zone”—pitchers are being put under a ton of pressure. One of three things will happen when a pitcher tries to work Bryce Harper outside. The pitch will hit its location, miss out of the strike zone, or miss over the middle of the plate. Only one of those scenarios entices Harper to take a hack and, as is evident from his swing plot, it ain’t the first two. Instead, it’s the scenario where Harper gets a pitch over the middle of the plate that he can crush. Spotting a pitch on the low-outside corner is hard, even if the strike zone is wider to a left-handed batter in this area. In 2017, Harper has been willing to ignore pitches to that location, because he knows a) the pitch might be too far off the plate and go for a ball, or b) even if it’s a strike, he wouldn’t be able to drive it, and the pitcher probably won’t be able to repeat the same location on the next pitch.

In the event of (b), Harper displays both the patience to lay off and the controlled aggressiveness to take advantage of the mistake that runs back inside. To this point in the season, we have seen pitches really struggle to hit that low-and-outside portion of the strike zone to Harper. Credit Harper for having the patience to cash in on mistake pitches in the part of the zone he considers to be his strength, but some amount of responsibility also lies on the shoulders of pitchers who have missed their spots against him:

The key portion of this strategy is that the hitter doesn’t just recognize a pitch in their preferred location as it comes across the plate; they pull the trigger, and swing at and drive that pitch. In a sense, after the “recognize your zone” portion of good pitch selection comes the “don’t miss your zone” portion. This is where Harper has excelled this season. We mentioned before that Harper isn’t missing pitches in the strike zone, but he has gotten even better at not missing pitches in his favorite portion of the zone. He waits for a pitch close to middle-middle and pounces on it.

The whole point of working a pitcher for a pitch in your wheelhouse is that you don’t miss the pitch in your wheelhouse. This is exactly what Harper has done, and he has done it to his immense benefit:

The final piece is seeing success once those pitches are put in play. You’d be hard-pressed to find a hitter that has had as much success on middle-middle pitches as Bryce Harper in 2017. His heatmap is incredible:

It is incredible to see how Harper has developed into one of the most patient-yet-powerful hitters in the game today. On pitches that Harper swings at within the strike zone, he is whiffing just 4.75 percent of the time. That is good enough for the 11th-lowest rate in the National League. Bryce Harper’s plate discipline formula within the strike zone resembles what Eric Thames is doing this season in Milwaukee, and is the best example for what a player looks like when locked in.

In 627 PA in 2016, Harper posted a .243/.373/.441 slash with a 112 wRC+. Relative to Harper’s overall body of work, it was the lowest single-season wRC+ of his career, and some claimed 2017 to a sort of rubber-match year when considering the Bonds-esque numbers Harper posted in 2015. The season is incredibly young, and Harper hasn’t even come to the plate 100 times yet. The small sample-size caveat to this whole thing is important, but the distinction for me is that Harper appears to have turned a corner in his discipline at the plate—something more reflective of an underlying change in his skill or patience, and therefore more meaningful, than his (admittedly outstanding) outcome stats are at this point in the season.

Now, is there a chance that Harper won’t be seeing the ball and zone this well come June or July? Absolutely. Harper could even deal with injuries (god forbid), or just lose his feel. Those are always possibilities, unfortunate as they may be. But in my mind, the latter is the only way this train is getting derailed. These changes are the result of gradual improvements since 2014, and I don’t think they’re going away, especially not while he’s healthy after an injury-riddled 2016 season.

So what does it mean to be locked in at the plate? In my opinion, it is using a patient approach at the plate to swing at a pitch in the zone you feel you can do most damage with. It is ignoring the famed “pitcher’s pitch” and pouncing on the “mistake pitch.” In short, it is whatever Bryce Harper has been doing this season.

All heatmaps taken from FanGraphs.