Nobody’s been able to stop ... Starlin Castro? A look at what the formerly light-hitting second baseman has done this season.

Never known as an offensive force, Yankees second baseman Starlin Castro has done nothing but mash to begin the 2017 season. In 88 plate appearances over 21 games, Castro is hitting a cool .361/.398/.578 with a 177 wRC+, easily the highest mark of his career to date. He already has been worth 0.8 fWAR, which is 72.7 percent of his total from 2016 (1.1).

This is quite a change from Castro’s past production. Before this spurt, Castro’s highest career wRC+ was 117, back in 2014. His highest fWAR total came way back in 2012, and he was only a league-average hitter that year (100 wRC+) but benefitted from excellent defense at the premier infield position.

Despite having been in the league since 2010, Castro is still young at 27, and he could be beginning to hit his offensive prime. And it isn’t even just Yankee Stadium’s doing; we know that because of his wRC+ — both park- and league-adjusted — showing that he’s almost 80% better than the league-average hitter at creating runs.

What has sparked such a drastic change in performance for what was always a light hitter? Like many hitters, Castro seems to have increased his launch angle.

Using Statcast data from Baseball Savant, we can see that Castro’s general launch angle in 2015 and 2016 was around 10 degrees. That is where he saw the most of his hits and a lot of his batted balls. But in 2017, Castro has increased his launch angle about five degrees upward, to around 15 degrees. While that may not seem like a lot, just this small change has proven to be a huge difference for many hitters around the league.

Check out the difference that this change in launch angle makes at different exit velocities.

Comparing 10 and 15 degree launch angles

Launch Angle Exit Velocity BA 1B% 2B% 3B% HR% Launch Angle Exit Velocity BA 1B% 2B% 3B% HR% 10 deg 80 MPH 0.500 48% 2% 0% 0% 10 deg 90 MPH 0.773 75% 3% 0% 0% 10 deg 100 MPH 0.936 75% 17% 2% 0% 15 deg 80 MPH 0.964 96% 0% 0% 0% 15 deg 90 MPH 0.865 74% 10% 2% 0% 15 deg 100 MPH 0.627 35% 23% 4% 0%

For 80- and 90-mph batted balls, a 15 degree launch angle posts a significantly better batting average, with balls hit at 80 MPH and 15 degree angles going for hits 96 percent of the time. A 10 degree launch angle does beat out the 15 degree angle in the 100 MPH category, but that’s likely due to the fact that balls at that high an angle hit that hard will be more likely to be caught by outfielders. On the flip side, hitting at the 15 degree angle does provide more pop, as you can see the extra-base hit numbers begin to jump a bit as you move down the chart.

And, that could be why Castro’s isolated power is so high. I sound like a broken record, but at .217, Castro’s ISO would be the highest mark of his career. He already has five home runs and three doubles in those 88 plate appearances. Over a 600-PA season, he’d be on pace for 34 bombs and 20 doubles, giving him the most total bases he’s ever recorded.

Plus, he’s making extremely hard contact, with his overall average exit velocity at 89.4 mph. Inside the zone, Castro is seeing average exit velocity numbers in the 90+ mph range, reaching as high as 97.6 mph right down the pipe. So a combination of a higher exit velocity and launch angle has created success for Castro thus far.

As always, we must ask the dreaded April question: Is it sustainable? A quick bit of research suggests it may be. Russell Carleton of Baseball Prospectus wrote about the stabilizing of exit velocity data last year, finding that these numbers begin to stabilize around 40 batted balls. Right now, Castro has had 66 balls put in play. That’s a good sign.

But, of course, it’s still April, and he could be riding a hot streak. I mean, he is riding a hot streak, and I must remind you that the question isn’t about whether he will cool down, it’s about to what extent will he. While I’d err on the side of caution, I am beginning to think that we are seeing a new Starlin Castro.

Other factors may also be involved here, and there is one that I want to briefly run down: plate discipline. Castro already has five walks this season, and his current walk rate of 5.7 percent would be the highest mark of his career since 2014. His strikeout rate—at 17.0 percent—would be a 2.3 percentage point drop off from last year, too. Both of these are definitely encouraging signs, but I’m not necessarily sure that Castro’s discipline has definitely improved.

First, as you may already be saying to yourself, Castro’s year-to-year numbers aren’t that different. Obviously, since he has a career 4.8 percent walk rate, a more noticeable change would be if he began walking in 10 percent of plate appearances… or even just 8 percent of plate appearances. But 5.7 percent? It’s really hard to call that a change.

And, while I’d agree with you there, I do believe Castro is being more selective at the plate, or is at the very least, making better contact (as I already talked about above). On pitches inside the strike zone, Castro is making contact 94.4 percent of the time, an 8.2 percentage point jump from last season. It’s the first time he’s been above the 90 percent plateau since 2012 — which, actually, was the third straight season he pulled that off. Coincidentally or not, 2010 through 2012 were three of the best offensive seasons of his career. His zone contact rate was at its consistent best, and so was his productivity.

However, then there’s 2014, a year when Castro posted the aforementioned 117 wRC+. That season, his zone contact rate was at 88.1 percent. The next year, in 2015, his izone contact rate was up to 89.9 percent, but he saw his wRC+ drop almost 40 points. How would I explain this? I really don’t know, but Castro’s small walk rate to begin with was cut in half over those two years, and that may have something to do with it.

Regardless of the state of his plate discipline, Starlin Castro is hitting the ball hard and with a better launch angle than he has ever posted in the past. That’s why it looks like he’s hitting the cover off the ball — he is. Castro’s plate discipline may be coming around with it, but since it’s darned old April, it’s still soon to tell.

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Devan Fink is a Featured Writer at Beyond The Box Score. You can follow him on Twitter at @DevanFink.