As LHB: .369 OBP/.326 SLG/.694 OPS in 1,761 at-bats
As RHB: .389 OBP/.483 SLG/.872 OPS in 656 at-bats
Castillo, like Berkman, has a 20% decrease in production, but unlike Berkman, Castillo hits better from the right side of the plate than he does from the left side. The problem is he is not a stellar hitter from either side.
As a leadoff hitter, Castillo's main job is to get on base, which he does well from each side of the plate. In the right-handed batter's box, at least he couples that with a .483 SLG. One cannot say the same thing about his life as a lefty batter. It is not simple feat for a player to have a slugging percentage lower than his on-base percentage, but Castillo has found a way to do it.
The Minnesota Twins would be well-advised to build an invisible dog electric fence around the lefty's batter's box, attach a collar around Castillo's neck, and shock him until he learns he is no longer allowed to bat left-handed.
As LHB: .375 OBP/.437 SLG/.812 OPS in 1,369 at-bats
As RHB: .310 OBP/.350 SLG/.660 OPS in 586 at-bats
Brian Roberts burst on the national scene last year when he posted splits of .459 OBP/.726 SLG/1.185 OPS, .440 OBP/.569 SLG/1.009 OPS, and .407 OBP/.534 SLG/.942 OPS over the first three months of the season. He cooled off during the course of the year, but still finished up the season with a very respectable line for a lead-off hitter of .387 OBP/.515 SLG/.903 OPS.
Now he is notorious for another reason, namely being a poor switch hitter. With a 19% drop-off in OPS, there is really very little reason for him to continue hitting from the right side of the plate. Not only does Roberts' OPS suffer when he bats righty, but his batting average also takes a precipitous drop from .305 BA to .237, a decrease of .68 points.
The fact that Roberts is just an average defensive second basemen makes the disparity between the sides of the plate even greater. A player whose offensive ability is his most important contribution to the team should not continue to hurt the team by batting so poorly when facing a particular handed pitcher.
As LHB: .345 OBP/.362 SLG/.708 OPS in 875 at-bats
As RHB: .380 OBP/.487 SLG/.867 OPS in 534 at-bats