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The curious platoon question of Martin Prado and Derek Dietrich

Martin Prado and Derek Dietrich will not platoon or split time at third base. Should they? That's a more complicated question than the deal at first base.

Kim Klement-USA TODAY Sports

Yesterday, we talked a little bit about the Miami Marlins failing to use the platoon advantage significantly in their recent past. The question of using it in the first base situation seems obvious; Justin Bour showed large splits in the minors and the big leagues, and new partner Chris Johnson has always hit lefties significantly better than righties.

However, could the same theory apply over at third base? Martin Prado is the incumbent, and his career line displays a reasonable split between batting against lefties and righties. The replacement would be Derek Dietrich, whom the Marlins have not afforded much opportunity but who hit well enough last season to warrant further looks.

Player, Career wRC+ vs LHP wRC+ vs RHP
Martin Prado 124 101
Derek Dietrich 70 112

Dietrich displays a very traditional exaggerated split against lefties in his limited experience (130 plate appearances) against the Major League versions of them. Meanwhile, Prado has always been above average for his career against righties, but much better against lefties. On the surface, this provides the perfect opportunity for a platoon, where a younger Dietrich can play the big half of the platoon and work more against right-handers and Prado can hit more exclusively against lefties.

The problem is in terms of defense. Last year, Prado was a Gold Glove-caliber defender at third base per the defensive numbers, and even if he was not as good as those numbers indicated, he has always been an above-average contributor at third base over his career. Meanwhile, Dietrich has been a negative defensively almost everywhere he went, including a short stint at third base last season. The defensive difference between these two players, no matter what it is, matters, and there is a tangible value to it, even if that value is more nebulous. We have a strong idea that Prado is a good defender and that Dietrich is a bad defender, but can we figure out what the cutoff point should be for the two?

I estimated the platoon projection using the same numbers and calculations I did to do last year's lineup analyses. Given the small sample with Dietrich, his results are more skewed towards the league average, and rightfully so; a lefty's career platoon edge takes about 1000 plate appearances to be halfway predictive of true talent, while a righty's takes 2200 plate appearances!

Player, Career Proj wOBA vs LHP Proj wOBA vs RHP
Martin Prado .330 .306
Derek Dietrich .289 .327

Those are about expected given these players' current projections. It should be noted that Prado and Dietrich are expected to hit about the same this season, with Dietrich's edge worth about five runs over an entire year. The question here, however, is how many more runs the Marlins could eke out if the Fish ran out a platoon rather than their expected alignment.

If the Marlins stuck to the most strict application of the platoon, it would likely end up in the big half facing righties abour 80 percent of the time, while the smaller half faced lefties at about 50 percent of the time. This is simply the nature of managing in which the platoon cannot fully eliminate same-handed pitchers from their diet. Along with injuries or other pinch-hitting duties, even the most strict small-half platoon partners like former Marlins utility man Jeff Baker have faced lefties and righties at about an even clip over their career. Meanwhile, Garrett Jones has faced lefties at a 15 to 20 percent rate in the last four years since being identified as a platoon guy. Brandon Moss has averaged a 79 percent rate of facing righties over his successful platoon career.

If we use these rates and give Dietrich two-thirds of the 700 plate appearances of playing time, we might expect a .320 wOBA for Dietrich overall and a .319 wOBA for Prado. As a combined group, we can essentially say that this tandem would put up a .320 wOBA. Compare that to the duo using Prado's numbers primarily, which would lead to a .314 wOBA over the course of the year. That difference of five points of wOBA is worth 2.5 runs a season, a small amount. Even if you take it closer to the extreme and give Dietrich a .325 wOBA in playing that often against just lefties, the difference would be closer to five runs a season.

Let's take that at five runs, or half a win, a year better than the Prado-primarily batting situation. That would be the breakeven point at which it would be worthwhile to run a platoon over the veteran holding a starting role. The difference is now in terms of defense. Here we have to make some assumptions. Knowing Prado has been a good defender but is aging, it may seem reasonable to make him a three-run defender over a full year at third base. Given that Dietrich has been below average at every position, it may not be unreasonable to predict a -5-run defender over a full year. A platoon of these two might be worth -2 runs over the course of the year, while a primarily-Prado run system would be worth about +2 runs. The difference between these two is at four runs a year based on this prediction.

If you take the maximal difference between Prado and Dietrich on offense, their defensive difference just misses the cutoff point. If you take a more maximal defensive approach, their offense just misses the breakeven point. In the end, it is likely that this is a close call and the numbers cannot do it justice. The Marlins trust Prado more than Dietrich, which is why they will go in their direction. There is certainly an argument to be made that this year's club would see some benefit in getting Dietrich more playing time versus right-handed pitchers at third base, even with his defensive deficiencies. However, if Prado is nailing it defensively like he did last season, their expected offensive differences just may not be large enough to warrant a change, especially as Prado really came on in the second half.

In the end, it may be a preference decision. I trust the offensive differences a little more, and I think the defense has more of a chance to trend towards the extremes than on the offensive side. My managerial preference would be to see Dietrich get more playing time versus righties, but not commit to a full platoon in which he sees the majority of the time. There may be some more appropriate breakeven point that is between a full platoon and a full bench treatment for the 26-year-old whom the Marlins need to assess for the long term.