Vladimir Guerrero Jr. is finally coming to the majors -- here's how to evaluate his early performance

After cutting a swath through every minor-league level and doing so against older competition, 20-year-old Vladimir Guerrero Jr. -- the consensus top prospect in all of baseball -- will make his MLB debut Friday for the Toronto Blue Jays against the Athletics.

Guerrero of course has the Hall of Fame bloodlines, and that plus his performance dossier to date has raised expectations. Accomplished, scout-lauded hitting prospects like Guerrero are the safest bets among farmhands, and the reasonable assumption is that he's going to develop into at least a useful big-league regular. His ceiling, though, is much higher -- that of an MVP contender. 

Obviously, it's going to be quite a while until we know whether Guerrero is going to live up to the ballyhoo on a sustained basis, but certain early indicators can hint at whether Guerrero is ready to thrive at the highest level right away. Can he contend for AL Rookie of the Year honors and maybe even helm a surprise run at relevance for the 2019 Blue Jays? Here's a couple of things you can look for in the early weeks of Vlad Jr.'s career that could provide, well, not an answer to those questions but rather the beginnings of an answer. Onward ... 

Is he commanding the strike zone?

Commanding the strike zone is a phenomenon we typically associate with pitchers, but it's just as vital to the batsman. On this front, Guerrero has thrived in the minors. At this writing, Guerrero across parts of four minor-league seasons has drawn 141 unintentional walks against 137 strikeouts. For someone with his power, registering more unintentional free passes than strikeouts is an impressive feat at any level. 

Framed another way, Guerrero in the minors has drawn an unintentional walk in 11.3 percent of his plate appearances, which is a strong figure (the unintentional walk rate at the MLB level this season is 8.7 percent). Meantime, he's struck out in just 10.9 percent of his plate appearances versus a 2019 MLB average K% of 23.3 percent. It would be one thing to see such figures from a slap-hitting table-setter, but Guerrero has cracked 120 extra-base hits in 286 minor-league games with an isolated slugging of .199. So often hitters trade frequent contact for hard contact, but Guerrero hasn't yet needed to cut such a bargain. 

The question is: Can he keep this up against the best pitchers in the world? We'll get an idea sooner than you might think. A few years ago, Russell Carleton discovered that K% "stabilizes" after just 60 plate appearances. This doesn't mean that you know all you need to know about a hitter's contact skills after just two weeks and change of regular playing time -- far from it. Rather -- and in layman's terms -- it starts to mean a bit more than you might think after 60 plate appearances. Walk rate (unintentional and intentional walks, BB%) takes about twice that long to stabilize. So is Guerrero after the first month or so in the majors striking out a good bit less than that MLB average of 23.3 percent while walking in at least 10 percent or so of his plate appearances? Then that's an early sign that the plate discipline he showed coming up through the system may be ready to translate right away. That will be important, since those tandem skills are vital to what Guerrero has done and should be able to do with the bat in his hands. 

Is he hitting the ball hard?

Not surprisingly, Guerrero is fully capable of knocking the innards out of the baseball. Witness this recent act of hitting violence: 

And the people say: Larduhmercy. Anyhow, we'll very soon get exit velocity readings on every ball Guerrero hits, and that will tell us a lot and do so pretty quickly. Early in the 2018 season, Rob Arthur, writing in The Athletic, pointed out that just a single batted ball can tell us a great deal about what a hitter is capable of and whether he's likely to exceed projections. Here's Arthur's concluding paragraph: 

Most sabermetricians will tell you to hold off on seriously considering a player's performance for a few months, or at least until Mike Trout begins to lead the league in WAR. But as our metrics improve, smaller and smaller sample sizes become meaningful. And occasionally, a player does something so exceptional that it commands attention. As you watch the young 2018 season unfold, forget batting average and home run totals. Instead, look for exit velocities close to 120.

So 120 mph or thereabouts appears to be the magic number. Speaking of which, consider the following two bits of Vlad-related content: 

Vlad Jr. exit velocity update: through 40 games, Guerrero's put more than 45 balls in play at 100+ mph. He recently hit one 119.6.

In MLB this season, only three batters have put a ball in play at 118+ mph — Carlos Gonzalez (118.3), Aaron Judge (118.1), and Mike Trout (118).

— Arden Zwelling (@ArdenZwelling) May 23, 2018

That's from last season, when Guerrero was 19, and that 119.6 mph indeed qualifies as "120 mph or thereabouts." Yes, it happened against minor-league pitching, but that's not of much importance when it comes to this particular measurement. Hitters are responsible for the vast majority of a batted ball's exit velocity, and that Guerrero was even capable of hitting a ball at 120-ish mph speaks multitudes about his capabilities. 

Next: 

Yep, that's a 117-mph ringing double in the Arizona Fall League All-Star Game off Trent Thornton, who coincidentally is now pitching for the Blue Jays. Now a couple of observations about those data: 

So his work down on the farm suggests that Guerrero is capable of striking the ball at mega-elite levels. If in the early going of his major-league career he starts clocking a few batted balls of, say, 118 mph or higher, then you'll know he's where he needs to be.

Right now, the SportsLine Projection Model (@SportsLine on Twitter) tabs Guerrero for a rookie slash line of .267/.338/.475, which is strong production, especially for a 20-year-old in the bigs (making the majors at such an age is itself a sign of future greatness). That, however, might actually be a bit bearish. Hitters who hit the ball as hard as Guerrero does tend to outperform most projections. If you see Guerrero pop up on that hardest hits leaderboard in the early weeks, which is an outcome that ranges from possible to very likely, then don't be surprised if he winds up with an AVG/OBP/SLG that's significantly better than his forecast.  

Is he hitting the ball in the air?

A hitter's fly-ball and ground-ball tendencies start to mean something fairly early. In Guerrero's case, in the minors he's put up a fly-ball percentage of 34.1 and a ground-ball percentage of 43.1. This season, MLB hitters have a fly-ball percentage of 36.7 and put balls on the ground at a 42.5 percent clip. So Guerrero is roughly average in that regard, albeit against minor-league hurlers. 

Major-league pitchers are major-league pitchers in part because of their ability to dodge the barrel of the bat and work against a hitter's swing plane. In that sense, it'll be telling to see whether Guerrero against MLB hurlers are able to tease more grounders out of him. This, of course, is an era in which most hitters -- especially those capable of hitting the ball hard -- focus on putting the ball in the air so as to do extra-base damage. Will Guerrero be able to quickly settle in at a launch angle of around 20 degrees, which is optimal for a high-exit velo batter? After three weeks or so, we should have some early returns on this front. 

If we're going to indulge in snap judgments of Vlad Jr. -- and, let's be honest, we're all going to do that -- then let's use the tools that at least tell us a little something. Things like batting average and even OBP and slugging take time to mean something, and indeed you can get fluke-y outcomes even over the span of an entire season. We have better options when the data sample is small. 

Let's recap, then, your roadmap to passing firm judgement on Vlad Jr. before you really should be doing that sort of thing ... 

Now let's kick back and see if one of the best hitting prospects of his generation turns into one of the best hitters of his generation. 

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