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It's now two years later and Casilla has indeed replaced Castillo as the Twins' second baseman and (sometimes) leadoff hitter, although the team's decision to trade Castillo pushed that timetable up about a half-season. Casilla stepping into the lineup for Castillo makes an already natural comparison even easier, because the similarities include name, size, place of birth, position defensively, offensive style, speed, and the ability to switch-hit. On the surface at least, they appear to be nearly identical.

Of course, just because diminutive speedsters from the Dominican Republic share many traits doesn't mean that they actually perform similarly on the field. Jose Canseco and Ozzie Canseco are identical twins--as opposed to Castillo and Casilla, who appear to be "identical Twins"--but Jose's 462-to-0 homer lead shows that they were anything but identical players. Rather than focus on the obvious similarities between Castillo and Casilla, let's examine how their on-field performances compare.

Let's begin with what they each did while playing at Single-A early in their pro careers:

SINGLE-A       AVG      OBP      SLG     IsoP     IsoD      BB%      SO%
Castillo      .326     .419     .362     .036     .093     13.9     12.7
Casilla       .327     .395     .409     .082     .068      8.8      9.8

Before diving into the above Single-A numbers, it's important to note than Castillo played there as a 19-year-old, whereas Casilla was 20 and 21 while at Single-A. That's an important distinction in terms of projecting development and makes a comparison of raw numbers somewhat less meaningful. However, it's interesting to note that they performed similarly well despite the age difference, posting high on-base percentages while hitting .326 and .327 respectively.

Castillo drew 58 percent more walks and struck out 23 percent more often, which shows that despite being a teenager he was significantly more patient at the plate and simply more able to work long counts. Casilla didn't show nearly the same type of plate discipline, but struck out significantly less, hit for twice as much power, and did better work on the bases. Castillo stole .46 bases per game at a 69-percent success rate, while Casilla stole .49 bases per game at an 81-percent success rate.

Next up is Double-A, where Castillo played as a 20-year-old and Casilla played as a 21-year-old:

DOUBLE-A       AVG      OBP      SLG     IsoP     IsoD      BB%      SO%
Castillo      .317     .411     .393     .076     .094     13.6     14.0
Casilla       .286     .366     .365     .079     .080      9.6     11.0

Along with a 31-point advantage in batting average, Castillo again showed far more plate discipline than Casilla by walking 42 percent more often. Casilla's power edge disappeared, but he followed up his Single-A performance by again striking out less often and doing far better work on the bases. Castillo stole .47 bases per game at a 65-percent clip, while Casilla stole .38 bases per game at an 80-percent clip.

Next up is Triple-A, where Castillo played at 21 and 22, and Casilla played at 22 earlier this season:

TRIPLE-A       AVG      OBP      SLG     IsoP     IsoD      BB%      SO%
Castillo      .303     .410     .347     .044     .107     15.3     14.9
Casilla       .267     .336     .334     .067     .069      9.3     14.1

Triple-A was pretty much the same story as Single-A and Double-A, with Castillo holding a 36-point edge in batting average while walking 65 percent more often. Casilla reclaimed a 55-percent power advantage, but his once-mighty edge in strikeouts shrunk to just five percent and he fell behind on the bases. Castillo stole .35 bases per game at a 70-percent success rate, while Casilla stole .26 bases per game at a 66-percent success rate.

Last but not least, let's compare big-league performances through the age of 22 (Casilla is currently seeing his first extended action in the majors, while Castillo saw multiple stints with the Marlins through the same age):

MAJORS         AVG      OBP      SLG     IsoP     IsoD      BB%      SO%
Castillo      .236     .312     .279     .043     .076      9.8     20.5
Casilla       .228     .279     .265     .037     .051      6.7     12.6

If nothing else, their respective major-league numbers through the age of 22 show that there's little reason to be overly concerned about Casilla's sub par performance with the Twins thus far. With that said, Castillo continued the minor-league trends by drawing 46 percent more walks and striking out 63 percent more often, and did so while completely closing the gap in power. Castillo stole .23 bases per game at a 72-percent clip, while Casilla has begun his career 8-for-9 swiping bases.

What does this all mean in terms of the popular Castillo-Casilla comparison? First, it means that the comparison is more apt for style than for substance. Castillo and Casilla are very similar physically and stylistically, but their actual on-field results haven't been nearly as close. Casilla has made better contact while hitting for more power, while Castillo has drawn far more walks while hitting for a much better batting average.

The numbers-to-numbers comparisons certainly don't show dissimilar players, but it's clear that truly duplicating Castillo's career will be extremely difficult because of the unique skill set involved. In other words, it's extraordinarily hard to draw a high number of walks while hitting for almost zero power, and the ability to do that while consistently hitting above .300 is what's made Castillo such a successful player. Casilla's track record suggests that he doesn't possess that same ability.

Casilla has shown significantly less plate discipline at every step along the way and in that sense his superior contact rate can be viewed as part of an inability to work long counts. Avoiding strikeouts is never a negative quality by itself, especially for a speedy player who lacks power, but for Casilla it's also a sign that he's far less able to extend at-bats and fight to get on base despite that lack of power than Castillo was at the same stages in his career.

Toss in lower batting averages throughout his track record and it seems unlikely that Casilla will match Castillo's .370 career on-base percentage in the majors. Of course, he looks capable of making up for some of that lost OBP with far more power. Casilla will never develop into a home-run threat, but unlike Castillo his track record hints at some semblance of extra-base pop potentially on the horizon. Castillo possesses a historic lack of power, while Casilla's lack of power looks to be of the non-historic variety.

Are Castillo and Casilla similar? Absolutely. In fact, they're probably among baseball's most similar pairs of players. However, Castillo possesses (or at least possessed) a set of offensive skills that make him unique in this era of baseball history, whereas Casilla's skill set is more common. Not every speedy, switch-hitting middle infielder who lacks power can bat .300 while coaxing walks in bunches, so don't expect Casilla to do that just because he resembles Castillo in many other ways.