Last year, Mike Trout was 20-years-old, and he did things that no other 20-year-old in history had ever accomplished. He’s the only 20-year-old in baseball history to post a +10 WAR season, and it wasn’t just driven by his positive fielding numbers, as his 166 wRC+ was the best hitting performance any 20-year-old has ever posted. It was an historic season in many ways, but it was also the kind of season that didn’t look repeatable.

His BABIP was .383, and both his fielding and baserunning numbers were among the best in the game, but all of those variables are heavily influenced by speed, and speed peaks very early. During his run last year, I repeatedly noted that I thought Trout would probably settle in as more of a +6 to +7 WAR player, because his defense and baserunning would regress faster than his offense would improve.

And, really, his BABIP, his defense, and his baserunning have regressed somewhat. Trout’s UZR is just +0.5 despite spending about half of his games in left field, his BABIP is down to .357, and he’s only stolen 16 bases this year after swiping 49 last season. Trout noticeably bulked up over the off-season, and he doesn’t appear to be quite as fast as he was last year. He’s still a burner, but he’s probably not in the fastest player in baseball conversation anymore. So, in that sense, my expectations for Trout regressing have been vindicated.

Except, you know, his wRC+ has fallen from 166 last year all the way down to 163 this year. The BABIP correction has essentially been canceled out by an improvement in his contact rate, so he’s just not striking out as often as he was last year and the increase in balls in play has allowed him to maintain his offensive levels from last season. And, while his stolen base totals are down, he’s still taking a ton of extra bases, which shows up in his league leading +3.3 UBR, the part of our baserunning calculation that measures value from advancing my means other than stealing a base. Trout had a +5.0 UBR last year, so he’s actually on pace to get more value from his non-steal baserunning this season than he did in 2012.

Last year, Trout was the best 20-year-old in baseball history. This year, his performance is going to give him a shot at being the best 21-year-old in baseball history.

Here’s the all-time age-21 leaderboard, with just the top ten seasons by WAR highlighted below.

Season Name G PA AVG OBP SLG wOBA wRC+ Fld BsR WAR 1917 Rogers Hornsby 145 589 0.327 0.385 0.484 0.416 162 18 0 9.4 1911 Joe Jackson 147 641 0.408 0.468 0.590 0.494 184 5 2 9.3 1953 Eddie Mathews 157 681 0.302 0.406 0.627 0.451 167 3 0 8.6 1929 Jimmie Foxx 149 638 0.354 0.463 0.625 0.480 177 4 -2 8.1 1980 Rickey Henderson 158 722 0.303 0.420 0.399 0.377 136 18 10 7.8 1972 Cesar Cedeno 139 625 0.320 0.385 0.537 0.413 163 2 4 7.8 2001 Albert Pujols 160 676 0.329 0.403 0.610 0.423 159 6 -1 7.2 1998 Andruw Jones 159 631 0.271 0.321 0.515 0.353 113 35 4 7.0 1991 Ken Griffey Jr. 153 633 0.327 0.399 0.527 0.399 148 7 1 6.9

(Fun side note: Trout’s 2013 season already ranks as the 42nd best age-21 season ever. By the All-Star break, there’s a good chance that his half season will have been more valuable than what guys like Mickey Mantle and Joe DiMaggio did in their entire age-21 season.)

While Hornsby comes out on top, Shoeless Joe is in a virtual tie for the top spot and isn’t as dependent on the fielding part of the calculation, and fielding numbers from 100 years ago shouldn’t be taken too literally. Hornsby was probably a really good defender, but was he good enough to make up for 78 points of wOBA in 52 fewer plate appearances? I don’t know, and there’s no way to know, but either way, you could say that the best age-21 season of all time is probably in the +9.5 WAR range.

Well, after last night’s performance, Trout is now at +4.3 WAR in 73 games, and that’s with some demerits for his defensive performance. If he sustained this exact performance and played in 88 of the Angels remaining 89 games, he would finish with +9.5 WAR. In other words, Trout is on pace to have the best age-21 season in history even with the fielding metrics not being particularly in love with his first half performance in the field.

Of course, defensive metrics can have big swings in small samples, and the reality is that Trout is probably still a very good defensive outfielder, especially when being compared to other left fielders. We shouldn’t continue to project Trout to be rated as a league average defensive outfielder, so if we work in some positive regression for his fielding, he doesn’t even have to keep hitting at this level to get to +9.5 WAR. And yet, there’s signs that his offense might be getting even better.

Here’s Trout’s offensive performances by month since his callup to the Majors last year:

Month Contact% BB% K% May, 2012 87% 9% 23% June, 2012 80% 7% 18% July, 2012 85% 11% 19% August, 2012 78% 10% 24% September, 2012 78% 15% 26% April, 2013 78% 10% 20% May, 2013 86% 11% 20% June, 2013 92% 14% 11%

As good as Trout was last year, he was that great while only making contact 82% of the time, and those contact issues carried over in April. His contact improved in May without being reflected in his strikeout rate, but in June, he’s hitting everything he swings at and the result is a dramatic drop-off in strikeouts. Basically, Trout is showing signs of dramatic improvement in the the one area you could kind of point to as a deficiency. A strikeout-free version of Mike Trout is essentially the perfect baseball player.

While changes in contact rate can be identified in smaller samples than in other outcome based metrics, we’re still dealing with just a few weeks of data here, but Trout should be expected to improve facets of his game given that he’s still at a point in his career where most players are working their way through A-ball. Even if the improvement is more incremental than a huge leap, an uptick in his contact rate is going to help offset BABIP swings. If he really can start making contact in the 85-90% range on a regular basis, with the rest of his skillset, then he’s a true talent +8 or +9 WAR player.

So, yeah, Mike Trout is pretty good at this baseball thing. Both ZIPS and Steamer project Trout for +4.1 WAR over the remainder of the year, which means he would finish at +8.4 WAR, which would be the fourth highest total for any player in their age-21 season. Expecting him to play 88 of the next 89 games and sustain this pace might be too much to ask. On the other hand, we’ve all been expecting Trout to stop playing at an all-time-great level for a while now, and when parts of his game get worse, he just makes up for it by getting better at other things.

I’ll always remember how amazing Albert Pujols’ 2001 debut was. Really, it was just a stunning season from a guy who spent the previous year in low-A ball. To just show up as a 21-year-old rookie and post a 159 wRC+ was incredible. Mike Trout, right now, is basically having Albert Pujols’ rookie season if Albert Pujols was also a great baserunner.

I think I’m going to stop putting a ceiling on what Mike Trout can do. The best 20-year-old ever might end the year as the best 21-year-old ever. We should appreciate what we’re seeing. No one has ever seen this before.