The book is out on Vladimir Guerrero Jr.

Last year, Guerrero hit 48 home runs and finished second in the AL MVP balloting. He had one of the best hitting years in Blue Jays history, although that’s even too limiting; he had one of the best years by any 22-year-old on any team in the post-war era. Given the massive hype that accompanied him as the son of a Hall of Famer with the same name, it felt less like “a breakout” and more like “an arrival,” the first of what would be 15 or so equally great years in a row on a path toward history.

Instead, we’re talking about how May 2022 is one of the weakest months in his short career. (His .706 OPS so far in May would be his third-worst.) We’re talking about how one of baseball’s most powerful sluggers went weeks -- weeks! -- without an extra-base hit. We’re talking about how the vaunted Blue Jays' offense has failed to lift off, and how the heart of their team is at the heart of the struggle.

We’re talking, really, about how pitchers decided they just weren’t going to let 2021 happen again, and so they haven’t.

When Guerrero went deep on Tuesday in St. Louis, it broke a run that shouldn’t have been possible. It was his first extra-base hit since May 5, a span during which 360 different hitters had posted at least one multiple-bagger. That list includes P.J. Higgins, Joe Dunand and Jose Herrera; it’s OK, at this point, to allow yourself to ask the question of whether we made those names up or not. (We did not.) So the next question is an obvious one: Why?

Let’s start with what we know it’s not, and that’s important, because there’s a whole lot of good still happening here.

It’s not a problem with contact. That’s the first thing you’d think of, right? A hitter struggles, you immediately run to strikeout rate. Not here. Guerrero has struck out just over 11% of the time in May. It’s one of the best marks in baseball. It’s the best of any month of his career. It’s extremely not this.

It’s not a problem with hard-hit. Last year, in his great season, he had a hard-hit rate of 55%. This year, in his lousy May, he has a hard-hit rate of … 56.9%. Nope! Not this either.

So that’s all promising, that Vlad Jr. is making a ton of contact, and making a ton of hard contact -- except that if that’s not leading to success, then you probably already know the issue, which is:

It is a problem with ground balls. Just like it was in 2019, really. Guerrero has put 60% of his batted balls this month on the ground, easily a career high. Last June, for example, when he had the best month of his career, that number was only 35%.

But you knew that, probably, even if you didn’t know the numbers. You’ve seen him hit grounder after grounder after grounder into opposing gloves this month, which -- no matter how hard hit -- opposing teams are extremely pleased to get. If you keep Guerrero from blasting a ball into the stratosphere, then you’ve won. (He’s hitting .219 with a .219 slugging percentage on grounders.)

Opposing pitchers, so far, have won. (In a sense; he's still hitting 30% better than league average. It's just that last year, he was 66% better than average.)

This didn’t happen by accident. What’s changed is how pitchers approach him, based on the respect he earned after last season. What’s changed, really, is how he approaches them back.

After what Guerrero did in 2021, pitchers were never just going to line up to have the same thing happen again, and they haven’t. They went to identify where he got his hard-hit balls in the air -- which, at the risk of oversimplifying too much, are what you’re trying to avoid from Guerrero at all costs -- and stopped giving him the pitches most likely to lead to that outcome.

Think of it like a checklist of problems to solve, for the men on the mound.

1. Vlad mashed four-seam fastballs in the zone
Solution: Fewer fastballs, thrown less in the zone and thrown harder

No batter against any pitch type was more successful than Guerrero was in 2021 against four-seam fastballs, against which he slugged .794 and hit 26 home runs. And then what happened?

In May, only three regular hitters are seeing four-seamers less often than Guerrero is (22%), a career monthly low for him. The fastballs he’s getting are thrown hard; if we include sinkers here, the average heater Vlad is seeing comes in at 94.5 mph, tied for the hardest in baseball. (This is something of a team-wide issue; two of his teammates are essentially tied with him, and the Blue Jays as an offense are challenged with velocity more than anyone else.)

So he’s getting fewer of the pitches he feasted on. That’s just the first part.

2. Vlad is more likely to hit higher pitches in the air
Solution: More pitches thrown low and outside

Last year, only 14 of the 78 extra-base hits he managed -- that’s 18% -- came in the lower third, or below. But nearly half of the ground balls he hit came in that area; you can see the difference in pitch location for the different types of batted balls.

Now, if you’re a pitcher, and you know that, what are you going to do? That’s right; when he doesn’t get a four-seamer, which he increasingly is not, the remaining pitches are in that low zone more than ever. He has just two extra-base hits in that low part of the zone and below all season long.

About a month ago, the story was that pitchers were refusing to throw him strikes -- on April 18, he’d seen the lowest rate of pitches in the zone of anyone -- and Guerrero, frustrated at the lack of mashable pitches, expanded his zone to get there. Because he’s so elite at making contact, he did, it’s just difficult to make loud contact outside the zone, so he mostly did not.

You could see it, in real time, on Tuesday against the Cardinals, when he saw 17 pitches, only three of which were four-seamers -- none remotely near the strike zone.

In the fourth inning, St. Louis reliever Nick Wittgren started Guerrero off with three pitches, all low and outside, non-competitive pitches. On 3-0, there wasn’t a prayer the next pitch was coming anywhere near his barrel. You knew it, and so did Vlad. He didn’t need to wait around to find out.

In the sixth, righty Drew VerHagen fell behind 3-1. The fifth pitch, a sinker, didn’t follow the script. It was belt high. Four hundred and thirty-eight feet later, it was in the stands.

VerHagen didn’t follow the book, and he paid for it. The next inning, he got another chance. This time the sinker was low, 1.9 feet off the ground, well lower than the 3.2 feet high the home run ball was.

Guerrero hit it hard, as he always does -- 108.2 mph. It hit the ground hard, too, bouncing twice on its way to third baseman Nolan Arenado, who completed the 5-3 putout. The difference in pitch height of just over 1 foot saved VerHagen about 430 feet worth of distance. Which is, of course, the plan.

The book is out. It’s up to Guerrero to force it to change.