The Yankees-White Sox trade is not without risk

The Yankees made a significant trade this week. They received Todd Frazier, David Robertson and Tommy Kahnle from the White Sox. The main prize they sent to Chicago was Blake Rutherford, along with lesser prospects Ian Clarkin and Tito Polo. The trade unquestionably makes them better this year, and probably in the future as well.

Frazier is an upgrade. He has a 102 wRC+, a real improvement on Garrett Cooper or whatever body the Yankees decide to throw at first base. He's also, obviously, a pure rental. The Yankees are acquiring Frazier to play baseball for two months or so. They're not giving up a strong prospect like Rutherford so they can employ a decent corner infielder for ten weeks.

They gave up Rutherford because this deal killed multiple birds with one trade. Robertson and Kahnle are both good right now, and Robertson is under contract for 2018, while Kahnle is under team control through 2020. The bullpen is better now than it was a week ago, and the 2018, 2019, and 2020 bullpens may have just gotten better as well.

That's where the upside of this deal lies, and it's that upside that required Brian Cashman to part with some prospect value. Robertson has a strong record and looks like a fine bet to be worth every bit of the $13 million he's owed in 2018. Kahnle has been legitimately excellent this season, and if he can maintain that form throughout his arbitration years, the Yankees will have a tremendous asset on their hands.

This is also where the risk lies. The Yankees got a pair of players that look pretty darn close to elite right now, but there is no promise they will be elite going forward. Robertson and Kahnle are relievers, and relievers are inherently volatile and difficult to predict.

In an article this past winter at FanGraphs, Craig Edwards discussed the very same David Robertson in the context of the riskiness of relievers. He noted that in 2016, the majority of relievers that posted more than 1 WAR (a strong total for a part-time pitcher) were actually projected for half a win or less prior to the season. In other words, relievers are so volatile that the bulk of relievers that had big seasons were forecast to be fairly middling, or worse, before the season.

Still, some relievers feel like they can just be penciled in for 70 innings, a heap of strikeouts, and a low ERA year in and year out. Mariano Rivera clearly fit that bill. Kenley Jansen is there now, as is Andrew Miller. There's something to be said for the truly elite reliever that is reliably outstanding all the time.

Yet the 2017 Yankees have lent a reminder that even dynamite relievers can have rough patches. Dellin Betances is walking nearly a batter per inning. Aroldis Chapman's ERA is inching towards four. Both of them would have been included in the paragraph preceding this one prior to the season, but their uneven performances demonstrate that even the best of the best relief aces can be unpredictable.

Even so, Betances and Chapman still have plenty of strong underlying statistical indicators and great stuff. They should be fine. Kahnle and Robertson aren't on the level of Betances and Jansen and Miller, though.

Kahnle has been stupendous, and it is with him that the real upside of this deal lies. His strikeout numbers are eye-popping, and they've come with a jump in velocity that makes it seem like he might be able to sustain this. Even so, his major league track record is all of 166 innings. Before 2016, he had a 4.04 ERA and 4.27 FIP. His outstanding 2017 has raised expectations, but we can't simply forget his nondescript performance before this year.

Robertson is more of a known quantity, but even being a known quantity has its drawbacks. To be a familiar quantity, you generally have to be around for a while. Likewise, Robertson is 32. He's been as good as ever at age-32, but he also posted a 116 ERA+ across his age-30 and 31 seasons. That's fine, but it's not particularly worth writing home about for a reliever.

The Yankees don't need to look far to see how risky relievers can be. Tyler Clippard was a salary dump in this deal, but he had a 1.06 ERA six weeks into the season. He had a 178 ERA+ as a Yankee in 2016 and was heralded as a stabilizing force in a bullpen that was left undermanned last season.

Why was that bullpen in need of stabilization? Because Miller and Chapman were gone, and unheralded journeymen like Richard Bleier and Anthony Swarzak were left to shoulder the load. Bleier, of course, has a 1.35 ERA with the Orioles this year, while Swarzak has a 2.45 ERA with the White Sox.

So Robertson and Kahnle may be great down the stretch this year, and they very well could be parts of formidable bullpens for years to come. They also aren’t quite elite, and should be subject to the same concerns regarding reliever volatility that most relievers are. That uncertainty is reflected in their projections: ZiPS pegs Robertson for a 3.35 ERA the rest of the way, and Kahnle for a 3.30 ERA, a step down for both from their current levels.

If Kahnle and Robertson play to their projections, this turns into a solid but unspectacular trade in which the Yankees got a few fine contributors in exchange for a fairly exciting outfield prospect, to go along with Clarkin and Polo. If Kahnle reverts closer to his pre-2017 form and Robertson declines a bit with age, suddenly, it will look as though the Yankees sacrificed one of their top prospects for an uninspiring return.

That’s the risk, and it’s a risk that is worth taking in order to strengthen the team for the pennant race this year and to improve the bullpen going forward. It’s just not as much of a slam dunk as the 2017 numbers of the players involved might suggest. If the Yankees can guarantee Robertson and Kahnle will be this good indefinitely, this deal is a big win. Given how unpredictable relief arms are, though, there’s just no feasible way to make that guarantee.