Let's go through the fancy numbers! (I know you don't think this allows for growth but it does. Guys can get better. It's just that they rarely get THAT much better overnight and a lot of times they are helped by out-of-whack luck on things they don't have much control over. Remember how we did this with Detwiler? Remember how he had a 0.90 ERA in his first 3 starts and we said it couldn't last and then in his next 3 starts he had an ERA of 4.50? That's why you need to pay attention here)
The Ranges - stats that can vary by pitcher but fall within a typical range.
BABIP (ranges between .250 - .325)
Career: .287 Last year: .288 This year : .209
Sorry, right here is a big reason ZNN is among the best pitchers in the NL right now. This early in the year, this is usually all it takes. Find a surprisingly low ERA and there is usually a surprisingly, and unsustainably, low BABIP behind it. Don't believe me? Jason Marquis has a 3.50 ERA and is 4-2. His BABIP is .223. This is going up.
Career: 9.0% Last year: 9.2% This year: 4.9%
Jordan has always been decent at keeping balls in the park. As you'll see below he's pitching in a way that we'd expect fewer homers. Still, 5% is too low. This will also rise.
Career: 75.4% Last year: 79.3% This year: 84.6%
Hey a pattern! Luck going completely for ZNN in a way that just can't be kept up.
You might be saying, "why can't these things be kept up?". Well, I can't give you a specific physical reason. What I can tell you is that the entire history of baseball featuring thousands of pitchers tells us a story. It tells us that outside of singular fluke years, the ranges fall where the ranges fall. Like take BABIP. The lowest pitcher in the history of the game with 1000 IP has a career BABIP of .240, the highest .330. That .240 (and those around it) are from a different era. Since the strike? It's .262 and it's Mariano Rivera. Unless you think ZNN is possibly the greatest pitcher of all time you can't believe he will keep these numbers up.
But that doesn't mean he's not pitching well or getting better. Let's now look at the personal fancy stats
The personal stats - is he getting better?
Career : 43.2% Last Year : 43.4% This Year : 50.3%
ZNN in the past has been more of a flyball pitcher. Flyball pitchers tend to live and die by the strike out and the walk because flyballs will become home runs, and you have to make sure you don't have runners on base when that happens. Groundball pitchers have a little more leeway. ZNN this year has been a pretty solid GB pitcher.
Career 7.30 / 2.07 Last Year : 7.04 / 1.98 This year : 6.00 / 1.59
He's also walking fewer people. While you don't want to see a drop in Ks the drop in walks is actually a bigger drop percentage wise (20% to 15%) and more important as he's moved from being a flyball guy to a ground ball guy so a drop in Ks matters less.
Pitch F/X data suggests that this isn't just fluky early season data. ZNN is pitching differently. Yes, more change-ups, but also more fastballs and fewer sliders. A better mix of offspeed stuff and more reliance on a top-notch fastball.
While the pitch effectiveness of the curve and the change remains mediocre the movement has improved on each. (thanks to brooksbaseball.net for the graphs)
And the whiffs on each pitch have increased dramatically.
So while it's likely that his biggest mistakes are still with these pitches (which would explain the mediocre pitch effectiveness) they are doing their jobs overall. They are keeping the hitters off balance so that the he can finish them off with weak contact on the fastball.
You see, before 2013 ZNN would try to finish off hitters with an off-speed pitch. Despite being only 23% of his total pitches, the slider accounted for 30+% of his strikeouts. The same thing was seen with the curve, about 12% of his pitches, but 17% of the strikeouts. Meanwhile with the fastball, you saw the opposite. He threw it over 60% of the time but it was only the "outcome" pitch (pitch where the AB ended) around 55% of the time and the K pitch around 50%.
In 2013 things have flipped. It's a little early to be sure if he's laying off the curve (he doesn't throw it that often) but the slider K percentage is down to 21%. The fastball has been thrown more (68% of the time) and its use as the outcome pitch has jumped dramatically (69%) as well as the K pitch (55%.)
This may not seem like much but there's a definite change here. The fastball,which is arguably his best pitch, is more entrenched as his out pitch. Which is as it should be.
Anyway, wrapping this all up what does this mean? It means that even though ZNN has gotten lucky, will experience some regression and is not likely to be in the Cy Young conversation at year's end, he is pitching better. He is throwing like a low-level #1 which, if Strasburg can pitch to his talent and Gio can pitch like last year, would give the Nats a 1-3 as good as anyone has had in a while.