As you've likely heard, Aaron Hicks came to the Twins a couple days ago and admitted something that fans had been begging to happen for a while now: Giving up switch-hitting. Being a natural right-handed hitter, Hicks picked up switch-hitting when he was in Little League, but it was clear that batting left-handed was always his weaker side. Thus far in the majors, that has been confirmed as he's hit .178/.259/.286 (.544 OPS) against right-handed pitchers but hit a far more tolerable .224/.330/.398 (.728 OPS) against lefties.
Virtually all teams have at least one switch hitter on their 40-man roster, with the point being that you should gain a platoon advantage against the pitcher. Every year, batters facing opposite-handed pitchers perform better than hitters that face the same side as the pitcher, so switch-hitting looks to capitalize on this advantage by always giving the batter the edge.
Unfortunately Hicks had been unable to find that edge. Twins fans had been calling for Aaron Hicks to swing exclusively from the right side during last season, but Hicks refused to make the switch and the Twins also felt it was a bad idea. The coaching staff and front office went so far to name other switch hitters that had made it work, but just because someone else could do it didn't mean that Hicks could, too.
The calls for him to give up his left-handed swing intensified when the Red Sox's Shane Victorino did that very thing last season. Due to injury, Victorino stopped swinging left-handed, but the truth was that he was a much better right-handed hitter anyway. Once the injury healed, Victorino kept his left-handed swing on the shelf, and last season he saw positive results. This year has been a different story, though it's interesting that he's shown more power against right-handed pitchers than he has against lefties thus far.
I get the point of switch-hitting, and I became curious to know how many players were actually successful with it. Therefore, I searched through every team's 40-man roster for all switch hitters, along with all major league free agents. I eliminated all players that had less than 1000 career plate appearances (to avoid sample size issues) and also sorted them in two ways. First, I wanted to see which players had platoon splits as extreme as Aaron Hicks', so I counted how many had a career OPS difference of at least .175 (close enough to Hicks' .184 difference). Second, I also sorted them by those that had a below-average OPS from either side of the plate, defined by being an OPS of less than .700.
In the first group, the results were rather disappointing but understandable. It's rare to find a switch hitter with a platoon split as awful as Hicks', because if you can't hit from one side of the plate, you either remain in the minor leagues or you just give up hitting from that side. I found a grand total of 2 hitters out of 40 (5%) that were as inept at hitting from one side of the plate compared to the other as Hicks (Daniel Nava and Jarrod Saltalamacchia). However, I found something far more interesting when I saw the players that were batting worse than a .700 OPS from either side of the plate. There were 19 out of 40 here (45%), showing that a good chunk of switch hitters are below average when they approach the plate.
Since that first number was disappointing, I decided to adjust it. Instead, I went with players that had a .100 OPS difference or more, since FanGraphs rates a .100 point swing as the thresholds between "Excellent," "Above Average" "Below Average," and "Poor." With this new cutoff, I found 8 of 40 (20%) that were at least .100 points worse as a lefty vs. righty or vice versa. That's certainly more than I found before, but it's still not very many.
From looking at this data, although many of us ridiculed the Twins for arguing that Hicks should stick to switch hitting, this evidence seems to support that notion. Most switch hitters are able to make it work and even if they can't muster a .700 OPS, most were still around .650 or better. Granted, I'm willing to admit that this research is subject to survivor bias, as I mentioned before. If you can't hit from both sides of the plate, you either give up switch-hitting or you just don't last in the major leagues. It's likely a good thing that Hicks made the switch, because if he hadn't, he likely would be joining the latter group shortly.
Google spreadsheet with data can be found here.