Somewhere in the middle innings a spring training game against the Twins, Ricky Horton mused that the Cardinals would soon be looking to move Yadier Molina to first base, the way that the Twins have done with Joe Mauer. It's a notion that's been floated many times before, and in Horton's defense, it's the kind of idle filler that's probably hard to avoid when you need to talk through three hours of a practice game.
But it's also a really bad idea.
We all know that professional squatting is a killer on the knees, so as great catchers age, the justification to move them to first is "to keep their bat in the lineup." But as we all learned in Positional Adjustment 101, the standard for a great bat at first base is quite a bit higher.
Last season, Molina's weighted on-base average (wOBA), a good catch-all for overall batting skill, was .317. That ranked 22nd among catchers, though still above the .310 MLB average for the position. Among first basemen, he would have ranked 41st in wOBA, well below the MLB average of .333. For context, Matt Adams put up a .337 wOBA.
Obviously, Yadi was hampered by the thumb injury last season, and there's hope that he will bounce back offensively. ZiPS projects a .336 wOBA, good for 8th among catchers. But still, this would only rank him 27th among first basemen, just behind Adams and the player who Horton saw as a model for Molina, Joe Mauer.
In his prime, Mauer had a bat that would play anywhere. In his MVP 2009 season, he led the AL in wOBA. But as his batting skills have declined, the value of those skills has been further eroded by his move to first base. In 2013, his last year primarily as a catcher, Fangraphs rated his offense as 26 runs above average. Last year, primarily as a first baseman, it was down to just seven. On the defensive side, he went from six runs above average behind the plate to eight runs below average at first.
The impact on defensive value would be even more dramatic with Molina. No other player - at any position - approaches his defensive value over the last ten years. He's only played 73 innings at first base, so it's far too small a sample to put much stock into, but the defensive metrics grade him as poor to maybe just touching average. And let's be honest, when you watch Molina, "lateral movement" is not exactly the first thing that comes to mind.
Versatility is always valuable, and there certainly could be times where circumstances make it reasonable for Molina to get a spot start at first, or shift there in extra innings, etc. But just because he can play there doesn't mean he should play there. Randall Cunningham was a hell of a punter, but you were still better off playing him at quarterback.
Yadi is an absolute, all-time Cardinals great. If they ever build a Mount Rushmore on top of ballpark village, they should put Yadi's face (and neck tattoos) on it. He transformed himself from a no-hit defensive wizard to an offensive force who, in his peak seasons, would have even been an above-average offensive first basemen. But at this point in his career, Yadi's value is again heavily weighted toward his skills behind the plate. His bat may still be above-average for a catcher, but if he's your primary option at first base, you need to acquire a better first baseman.