The best statistics, be they evaluative or predictive, try to remove as much noise as possible from the equation. FIP, for example, focuses only on the things a pitcher can actually control, rather than the defense or the bad luck behind him on the field.
But there is a presumption upon which we’re tacitly resting when we use even the best statistics to compare players: over the course of a season, or many seasons, the caliber of opponents faced will more or less even out. Roughly-speaking, that’s true, especially when you adjust performance to account for ballpark factors and league.
But “roughly-speaking” isn’t the same thing as “precisely-speaking.” And although we can review statistics for guys like Cole Hamels, Jon Lester, Max Scherzer, and James Shields to compare their performance in a very nearly apples-to-apples kind of way, if you really want to get into the nitty gritty, it’s worth digging in on the opponents these guys actually faced in recent years.
That is the predicate for Jeff Sullivan’s latest at FanGraphs, and although all of this seems so obvious, it’s an exercise in which we rarely actually engage. Sullivan did it for the top available pitchers this year – Hamels, Lester, Scherzer, Shields – with a particular focus on how Hamels, the only one of the four for which a team would have to trade. Obviously that is of particular interest to the Cubs, given their interest in acquiring an impact arm this offseason.
Sullivan takes a deep look at the quality of opponents faced by each pitcher over the past three seasons by utilizing wRC+ (which means league has already been factored in). The summary chart, which shows the composite batter each pitcher has faced, will hopefully tease you sufficiently to read Sullivan’s piece:
On the whole, Lester, Scherzer, and Shields have more or less faced average hitters – that’s what you’d expect. Hamels, by contrast, has had a disproportionately easier slate the last three years.
Now, let’s be clear: that doesn’t make Hamels a bad pitcher, and doesn’t mean he’s not still a quality trade target. As Sullivan rightly points out, it doesn’t take anything away from the stuff or the durability or the experience. It does, however, mean you have to regard Hamels’ results a little more cautiously, especially if you’re trying to compare them to the results of other available pitchers.
In the end, I think it’s worth reading Sullivan’s piece as the start of a conversation. There are caveats aplenty (for example, the caliber of opponents faced has not been adjusted to account for the fact that those opponents may, themselves, have faced a disproportionately tougher slate of pitchers over the past three years, thus skewing their own results, making them look like lighter hitters than they might otherwise be).
I don’t think you can look at this and say, “Ah ha! Hamels is worth even less than we already thought!” But this is a conversation worth having.