What the hell is the matter with Bryce Harper?

Bursitis.

Oh, you wanted more? Fine:

Bryce Harper doesn’t know how to play outfield very well yet. He makes up for this by being unbelievably fast. But where his bad route to a ball intersects with a wall, that same speed results in painful collisions.

That’s heresy, right? How dare I impugn the defensive skills of the National League’s fifth-best outfielder (by UZR) in 2012? Yes, Bryce Harper posted a ridiculous 9.5 UZR in 2012–that is, his outfield defense prevented 9.5 runs from scoring on the 2012 Nats. That’s pretty good, right?

Sure. But let’s remember that UZR is a highly unstable measure of defensive ability–that is, we need a pretty big sample size to be sure of what we’re looking at:

How many UZR opportunities do you need for UZR to be reliable? There isn’t any magic number. If I asked you how many AB you need before a player’s BA becomes reliable, you would likely answer, “I don’t know. The more the merrier I guess.” That is true with UZR and with all metrics. Of course, for some metrics, you need more or less data than for other metrics for an equivalent reliability. It depends on the sampling error and the spread in underlying talent, and other things that are inherent in that metric. Most of you are familiar with OPS, on base percentage plus slugging average. That is a very reliable metric even after one season of performance, or around 600 PA. In fact, the year-to-year correlation of OPS for full-time players, somewhat of a proxy for reliability, is almost .7. UZR, in contrast, depending on the position, has a year-to-year correlation of around .5. So a year of OPS data is roughly equivalent to a year and half to two years of UZR.

This makes intuitive sense, in a way. To gather information about a player’s defense, we have to put a ball in play somewhere near that player and give him a chance to make a defensive play. In some cases, that happens pretty often–think of a second baseman or a shortstop taking ground balls. Other times, it’s less often–think of an outfielder (like, say, Harper!) standing around as his starting pitcher (like, say, Strasburg!) strikes out batter after batter.

All of this is to say that even though UZR says Harper likely saved 9.5 runs for the 2012 Nats, that might not really be the truest measure of Harper’s defensive prowess in the outfield–although, again, it’s the best we can do for now.

But let’s just take the one year of data and look at it  more closely, OK?

Now, UZR is broken up into components, each of which makes sense if you imagine yourself playing baseball. First, as the ball is put in play, you have to react to the ball, get to where it’s going, and put yourself in a position to make the play. The distance you cover to get to that ball is your range. Thus, the runs that you save because you can get to the ball (instead of letting it go by you) are Range runs, denoted RngR. Bigger is better here–this means you’re actually getting to the ball and getting a glove on it. That’s good news for your ball club.

Next, once you’ve got the ball, you might need to throw it somewhere in a hurry. Maybe you need to turn a double play, or maybe you need to hit a cutoff man, or maybe you’re trying to gun down a runner at the plate. You need a pretty good and accurate arm to do any of those things. The runs you save because of your good and accurate arm are Arm runs, denoted ARM.

Finally, things don’t always go your way. Maybe you get to the ball, then boot it. Or maybe your arm is strong, but not accurate; or accurate, but nowhere near strong enough. To err is human, of course. Runs you cost your team because of your errors are–shocker–error runs, denoted ErrR.

Now, let’s look at each of those components for 2012 Bryce Harper. Harper has 5.4 RngR, which tells us that he’s got pretty good range for an outfielder. His arm is absurd: 6.2 ARM,  best in the National League in 2012. He does goof every so often, though, giving up -2.1 ErrR. That all adds up to his 9.5 UZR.

Now let’s do the hack thing and compare Harper to Mike Trout, another phenomenal young outfielder.

Trout posts a higher UZR of 13.3, fourth-best in the American League in 2012. What’s interesting is that he does this despite a not-so-great ARM (-3.8). So, if Trout costs his team runs with a weak/inaccurate arm, whence comes this outrageous defensive skill? Well, Trout doesn’t make many mistakes. In fact, he makes fewer mistakes than average, so that’s worth 0.4 ErrR. The real story is that Trout has absurd range, with RngR of 16.7–best in the American League!

Now, think about what that means, for a second. What does it mean when we say that an outfielder has good range? It means he gets to balls that other outfielders might not be able to reach. There are three parts to fielding a ball in play in the outfield: first, you have to know the ball is coming to you. Then, you need to figure out where that ball is going to be, and how best to get there. Finally, you have to run to that spot and make the play.

Mike Trout has been playing the outfield for quite some time. He played the outfield as an amateur. He has, in his short life thus far, seen many more balls hit towards him in the outfield than Bryce Harper has. No wonder, too– Harper was an catcher as an amateur, and was only turned into an outfielder after he turned professional.

Now, Trout and Harper are built similarly. I don’t have the data, but let’s assume that they have similar reaction times. They can see equally well. They run more or less the same speed (fast!), jump more or less the same height (high!). I submit that the vast difference between Harper and Trout’s range has nothing to do with the raw physical part of fielding–the running to where the ball is going to be. It has everything to do with the first and second parts of the process–seeing the ball and picking the best route to the ball.

This is a long way of saying that Harper’s propensity to run into, at, or through outfield walls has nothing at all to do with his willingness to play hard, or play “the right way,” or whatever. Harper runs into walls, or pulls up at warning tracks, or sprints towards fly balls in the gap because he just doesn’t know where he is on the outfield. He makes up for his lack of skill by employing that prodigious physical gift of speed. It is a testament to Harper’s raw speed that his range is as good as it is at all.

The trouble is, of course, when those sub-optimal routes, taken at breath-taking speed, intersect with walls. That’s why he has bursitis now.

The good news here is that there is every indication that Harper will learn to be a better outfielder as he gains more experience. This is exciting, because if he can get better jumps on balls and make fewer mistakes, he can bring his absurdly powerful arm into play even more often.

Bryce Harper is good at baseball. He is not yet good at playing outfield. He is probably going to become very good at that soon, though–and that will be fun to watch.

Again, notice: this isn’t about Harper’s mentality, or whether he’s playing “too hard,” or whether he believes he can blast through walls like the goddamn Kool-Aid Man. This is just about a 20 year old kid learning to play baseball better tomorrow than he did today.

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