When you start your career the way Domingo Santana did, you don't always get a second chance.
In a brief taste of the big leagues with Houston in 2014, Santana struck out 14 times in 18 plate appearances, a shocking 77.8 percent strikeout rate. He continued his whiff-happy ways with the Astros in limited playing time in 2015, striking out 17 more times in 39 plate appearances. When Santana was eventually sent to Milwaukee in the deal that sent Carlos Gomez and Mike Fiers south, his Houston career was over with a 52 percent strikeout rate.
Even in today's strikeout-friendly climate, that's nearly twice as much as any hitter can stand to carry. But less than a year later, Santana has settled in as Milwaukee's starting right fielder, and he's made one big change that has led to two huge outcomes: he's stopped swinging at terrible pitches. That may sound overly simplistic, but it's true. As an Astro, Santana went after 32.5 percent of pitches outside the zone. With the Brewers last year following the trade, it was down to 23.7 percent. This year, it's down all the way to 15.2 percent.
If that sounds good, it is. It's very good. It's practically elite, in the sense that of the 194 qualified hitters this year, he's essentially tied for second-best in terms of plate discipline:
2016 swing percentage outside the strike zone
1. Jose Bautista, 14.5 percent
2 (tie). Christian Yelich, 15.1 percent
2 (tie). Brett Gardner, 15.1 percent
4. Santana, 15.2 percent
5. John Jaso 15.5 percent
As a result, Santana has cut down the strikeouts to something more manageable. That 52 percent whiff rate with Houston dropped to 31.7 percent with Milwaukee in 2015, and to 29.5 percent so far in 2016. Beyond that, he's changed his hitting approach so much that's actually atop a 2016 leaderboard for something far more resembling the right reasons: No one has hit the ball harder this year, compared to last, than Santana.
As you'd expect, "swinging at better pitches" and "hitting the ball harder" are inexorably intertwined, as we showed here in February. Last year, hitters who made contact inside the zone had a Statcast™ exit velocity 7.8 mph harder than those who made contact outside the zone; a .300 batting average inside the zone became a .188 average outside of it. It's the most important thing a hitter can do.
So when we say that Santana's new-found plate discipline has made a huge impact, we mean it. Let's look at 2016's biggest exit velocity gainers, through Monday's games, and use 30 batted balls as a minimum, leaving us with 218 hitters to look at.

That 96.3 mph mark isn't just the best on this list, it's the highest mark of any hitter so far with 30 batted balls, beating out some impressive names right behind Santana -- the red-hot Mark Trumbo (95.5) and hitting stars Ryan Zimmerman and Miguel Cabrera (each 95.3) and Giancarlo Stanton (95.2).
So is this the "real" Santana? Is any of this meaningful so early in the season? Last week on the Statcast™ podcast, we discussed exactly that, delving into how many batted balls you'd need to see before there was enough of a sample to take any meaning from it, and the initial studies show that perhaps 40 is a number that approaches reliability. Santana, as it happens, has exactly 40 batted balls. That's not to say this is what he will be, it just seems like enough to say this is what he has been, in a way that you wouldn't really say someone who was 1-for-2 in two plate appearances was truly a ".500 hitter."
Now, it's rare to see plate discipline improve this drastically -- not, of course, that he ever had any meaningful playing time with Houston -- but Santana is the youngest hitter on the Brewers, and it does appear that this is a team effort. One year after being the most wildly undisciplined offensive team in the Majors, the 2016 Brewers have taken a complete 180 on that front: 
2015-16 Brewers, team offense ranks, swing percentage
2015 -- 1st/tie (49.5 percent)
2016 -- 30th (41.3 percent) 
That's not instantly a good thing by itself, because we've seen the value of being aggressive. Except that when you look just at swings on pitches outside the zone...
2015-16 Brewers, team offense ranks, swing outside the zone percentage
2015 -- 1st (34.8 percent)
2016 -- 30th (24.2 percent)
...and if you think that's a massive difference, you're right. This sort of data goes back to 2007, so we have 300 team seasons on record -- 30 teams times 10 seasons apiece, including 2016.
2007-16 MLB ranks, swing outside the zone percentage
1. 2015 Brewers, 34.8 percent
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[Literally 297 other teams]
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299. 2016 Brewers, 24.2 percent
300. 2007 Athletics, 23.3 percent
So sure, maybe Santana is gaining familiarity with the zone as he gains experience. Maybe he was lucky enough to land on a team that's had the most shocking plate discipline turnaround of all time in the first year of the David Stearns era. Maybe they'd do better to be more aggressive in the zone, since they have the third-lowest zone swing percentage at pitches you generally want to hit.
Gif: Domingo Santana home run MIL
Really, though, it's a combination of all of it. Now Santana, the prospect who came up too soon and failed so badly that it was easy to see him never coming back at all, has a 110 wRC+ in parts of two seasons for the Brewers, read as "10 percent above league average." Let's say he maintains that, which is self-admittedly a huge assumption. Since 2000, only eight right fielders have managed a 110 wRC+ at 23 or younger. The names are impressive: Bryce Harper, Stanton, Yasiel Puig, Jay Bruce and Jason Heyward among them.
That's not to say that's what Santana will be. He's not even 300 plate appearances into his career, and a good portion of those were unimpressive. If you're looking for signs of progress, though, you've got them, and that's the entire point of the 2016 Brewers season. Santana has figured out the key to hitting, which is not helping the pitcher. In most cases, that's far easier said than done. So far, Santana is doing it.