In what turned out to be his final year in Arizona before Thursday's trade to St. Louis, Paul Goldschmidt did more or less what he always does.
The Cardinals' blockbuster new addition batted .290/.389/.533 (145 wRC+), bringing his career line to … .297/.398/.532 (144 wRC+). Goldschmidt produced 5.1 wins above replacement (WAR), per FanGraphs, after producing 5.0 and 5.2 in 2016 and '17. Sounds about right.
• Cards trade for Goldschmidt to snag elite bat
But within that steady, Goldschmidt-like campaign, there were some odd fluctuations. Whether due to the installation of a humidor at hitter-friendly Chase Field, random variation, or something else entirely, Goldschmidt was barely above average at home (108 wRC+). Yet he was a top-three hitter in MLB on the road (180 wRC+), giving him some of the game's most extreme splits in that area.
Then there was the down-and-up course the six-time All-Star first baseman's year took, as he hit rock bottom in May before soaring back into the National League MVP race. With Goldschmidt joining a Cardinals club intent on ending a three-season postseason drought, it's worth examining the peaks and valleys he experienced in 2018 to see what went wrong -- and then right.
After a solid March/April, Goldschmidt batted just .144/.252/.278 over 26 games in May, before recovering with a .330/.420/.602 line the rest of the way. For some context on that Jekyll and Hyde act, consider Goldschmidt's best and worst offensive months, by park-adjusted wRC+, in which 100 is league average.
Goldschmidt's lowest monthly wRC+
Min. 75 PA (41 qualified months)

1. Sept. 2017: 37
   2. May 2018: 46
   
2. Aug. 2012: 88
   4. Sept. 2018: 103
   
3. Aug. 2015: 111
   Goldschmidt's highest monthly wRC+
   Min. 75 PA (41 qualified months)
   
4. May 2015: 216
   2. June 2018: 214
   
5. May 2013: 207
   
6. June 2012: 200
   5. Aug. 2018: 194
   He followed up his second-worst month at the plate with his second best, going from hitting like a backup catcher to hitting like peak Ted Williams. And Goldschmidt maintained a torrid pace all the way into mid-September before finally slumping over his final dozen games.

This is somewhat about quality of contact: Goldschmidt hit the ball harder and got it in the air more often over the last fourth months of the season. And it may be a little about luck: He underperformed his expected numbers in May, according to Statcast™, and slightly exceeded them afterward.
But what really stands out about Goldschmidt's 2018 is the degree to which he was in control of his plate appearances. In other words, the count plays a huge role in the outcome of any particular pitch. Early in the season, the count was working Goldschmidt, instead of the other way around.
Plate appearances going to 0-1
March-May: 61.6 percent
June-Sept.: 46.4 percent
In that first time period, no regular hitter was falling behind 0-1 in a higher percentage of plate appearances than Goldschmidt. During the latter period, he ranked in the bottom 25 percent of the league.
It wasn't so much what Goldschmidt was or wasn't swinging at, so much as what happened when he did. Through May, the four-time Silver Slugger winner was missing or fouling off about 80 percent of the first-pitch swings he took in the strike zone. That put him among the MLB leaders, but he dropped that all the way to 60 percent over the rest of the season.
Why does that matter? Goldschmidt owns a .795 slugging percentage when putting the first pitch in play, but even a hitter of his caliber is fighting uphill after an 0-1 count. His career slash line following a first-pitch strike is a modest .261/.325/.449.
It wasn't just first pitches. Through May, nearly 200 batters swung at 200 or more in-zone offerings, regardless of count, and only six missed or fouled them off at a higher rate than Goldschmidt (67.8 percent):
1. Ian Happ: 72.9 percent
2. Mike Zunino: 71.6 percent
3. Jorge Alfaro: 71.5 percent
4. Matt Davidson: 69.6 percent
5. Lewis Brinson: 68.4 percent
6. Chris Davis: 67.9 percent
That's not exactly encouraging company to keep. All six eventually finished the year ranked among the MLB leaders in strikeout rate, and none were much more than league-average hitters, with Davis and Brinson ranking at the bottom of the league.

Goldschmidt isn't one to share much about his process with the public, but after his rebound resulted in another All-Star selection, he credited his extensive video and cage work with D-backs coaches. The group delved into both approach and mechanics.
"It's hard to explain," Goldschmidt said, via MLB.com's Steve Gilbert. "I think the biggest thing was I was able to get in a better hitting position, which allows everything to work together off that. Whereas if you're not in a good hitting position, it can lead to your head moving, your front shoulder coming out, your timing being off, whatever. It all reverts back to your base -- being in a good position to hit. It's not like we didn't know that, or do things to try and get back to that. I guarantee we tried everything, and finally something just really clicked."
Whatever fix or fixes they found worked.
Goldschmidt took greater advantage of hittable pitches, got himself into more favorable counts and cut a soaring strikeout rate back to about his career average. The production followed, with a 170 wRC+ that ranked third in the NL, behind only MVP Christian Yelich and Player Page for Max Muncy.
Six months after Goldschmidt reached the low point of his season and inspired some consternation about his superstar status, the Cardinals gave up three promising young players for one guaranteed year of his services. St. Louis' hopes for a postseason return could hinge on that miserable May remaining firmly in the rearview mirror.