Trout's defensive marks limited by chances

Despite missing seven weeks due to injury, Mike Trout still very much has a path to win the American League Most Valuable Player Award, primarily because he's added so much value with his bat (.315/.452/.638) as the Angels hang around in the AL Wild Card race.
But value, as we know, is about far more than just hitting, and defense matters. So why, after a career of highlight catches and award nominations, are Trout's fielding numbers down in 2017? 
It's true across the board, really. Defensive Runs Saved sees Trout as having saved just one run, as opposed to six last year. By Ultimate Zone Rating, it's -5.3. And by Outs Above Average, the newest Statcast™ outfield range metric, he's at -4, tied just for 95th of the 121 outfielders with 100 opportunities. (Compare that to Byron Buxton's MLB-leading +24 OAA for context).
So regardless of which metric you prefer, Trout hasn't been seen as adding a ton of defensive value this year. In fact, his best catch all year had a relatively high 65 percent Catch Probability. It's good, not great, by the standards of "a player's best catch."

But why? Generally, the first place you'd look when you see an outfielder decline in production is that he's gotten slower as he's aged or has been injured, yet that's not the case here. We measure foot speed with Sprint Speed -- feet per second in a player's fastest one-second window -- where 27 feet per second is the league average. In 2015, Trout was an above-average 28.6 feet per second; in '16, he was a nearly-identical 28.4 feet per second; this year, it's still 28.4 feet per second. If he's not Buxton or Billy Hamilton (30.1 feet per second), he's still fast and is not getting slower. So it's not that.
Nor is it an abundance of mistakes, either. For what little errors are worth, Trout has committed just one this year, and even that was him letting a grounder skip by rather than him failing to track down a catchable fly ball.
So what is it? It's all about the difficult opportunities -- or lack thereof -- and what happens on them.
Using our new Outs Above Average tools, we can dig into that a little more deeply. Looking at the same list of 121 outfielders with 100 chances this year, Trout has the highest Expected Catch Probability at 89 percent.
What that means is that based on the difficulty of batted balls hit to him, an average fielder would be expected to make the play 89 percent of the time. That's well higher than the Major League average of 83 percent, and it's far higher than what Robbie Grossman of the Twins is seeing, as he's all the way at the bottom, getting opportunities an average fielder would make only 75 percent of the time.
Now this could be due to any number of things. It could be that Trout (or his coaches) has done an excellent job of pre-play positioning. It could be about the batted balls allowed by Angels pitchers, who have surrendered the fifth-most homers in baseball, thus removing plenty of potentially difficult catches. It could also just be about pure random batted-ball luck.  In 2016, Trout's Expected Catch Probability was a more middle-of-the-pack 85 percent.

Trout's Actual Catch Percentage, by the way, is 88 percent, so he's basically performing as an average outfielder would -- given his 89 percent Expected, he's essentially even in terms of adding or subtracting value.
But let's break this down into two sets of plays -- easy and hard. For our purposes, we'll call the "easy" plays ones that have a 70 percent Catch Probability or higher; these are the cans of corn that most competent Major League outfielders can easily pull in, and they do -- 97 percent of these balls turn into outs. (If this seems confusing, remember this: catch probability is not evenly distributed, and a disproportionate number of fly balls have a catch probability above 90 percent.)

Trout aligns with that perfectly; he's seen 213 of these "easy" plays, and he's caught 209 of them, converting 98 percent.
It's far different, however, with the "hard" plays. As we said, Trout simply hasn't received a ton of opportunities -- just 25, which ties him for 89th most. Obviously, he missed several weeks of play, and that's a factor, but it's not just that. Nick Williams has 33, and he was only called up in late June. Bryce Harper has 33 as well, and he's missed nearly as much time as Trout did. Put another way, Mookie Betts gets one of these tougher plays an average of every 1.7 games, Ender Inciarte gets one every 1.8 games, and Trout gets one only every 2.8 games.

So it's that, to start with. Even Buxton can't will a great opportunity to come out of thin air. But it's also that of the 93 fielders who have been presented with at least 25 of these tougher chances, Trout is one of only three who hasn't converted one, along with Matt Kemp and Melky Cabrera.
Let's take a look at a few. For example, in early April, Khris Davis hit a liner to center where it appeared Trout misjudged the wall, pulling up on a ball with a 35 percent Catch Probability.

"Little surprised that he stopped at that one," said the Angels' broadcast. "I thought Trout had an opportunity."
Earlier this month, Trout had a shot to get a 29 percent ball off the bat of Yuli Gurriel, which we can show compared to a nearly identical 32 percent Inciarte play from April. Trout pulled up, but Inciarte aggressively made the play.

If these look like difficult chances, they're supposed to be; we showed, after all, that on the easier plays, Trout is performing just like everyone else. And of course, within this group, not all are created equally. For example, one play Trout didn't come up with was this liner by Justin Smoak in April, a ball that had a mere six percent Catch Probability. It's extremely difficult to make that catch, though not impossible, since Kevin Pillar made a similar play last summer.
But we can account for that, too, by looking at Expected Catch Percentage on just these more difficult plays. On the easy plays, the expectation was that Trout would catch 97 percent of the chances, and he caught 98 percent. On these harder plays, the expectation was that he'd catch 23 percent of them, yet he's caught zero -- tied with Kemp for the largest negative differential. By comparison, the tougher balls hit to Kevin Kiermaier had a similar expected conversion rate of 30 percent, but he tracked down 56 percent of them, the largest positive improvement, showing how elite he is. 
So why don't the metrics favor Trout as much this year? It's mostly because he simply hasn't received the same opportunities other outfielders have -- and partially because when he has, he's not made the great plays we're used to seeing from him. Trout is still very much in the AL MVP Award conversation, of course. It's just that this year, it's his bat that will carry him more than his all-around game.