Dansby Swanson is Back, and the Numbers Show How Much Cubs Missed Him

Just in time for a potential postseason run, Dansby Swanson is back. The Cubs’ starting shortstop and defensive stalwart returned to the lineup on Friday in Cincinnati after missing roughly one month with an oblique injury. The Cubs should be incredibly grateful he made a return so quickly. When he went down with his injury, our own Matthew Trueblood wrote that “although Swanson has been his inconsistent self at the plate this year, his value as a defender at shortstop is virtually unparalleled.” It wasn't hard to see that value (or, rather, the lack thereof) during his absence.

Exactly how much did his one month on the injured list end up hurting the North Siders? We can reach a rough approximation of this using the Fielding Run Value stat at Baseball Savant. In the 125 games that they played prior to Swanson’s injury, the Cubs led all of baseball in this statistic, having saved 61 runs above average. That was a whopping 23 runs more than the second-place Cardinals. 

In their 27 games without him, they saved seven runs above average, just eighth-best in baseball. They went from saving almost half of a run per game (above average) to about a quarter of a run. That feels like a significant drop. 

Defense, much like baseball as a whole, is very much a team endeavor, even though it's often perceived as individual effort. Shortstop is certainly one of the most important defensive positions out there, though there are still eight other guys that all have a job to do. Is it fair to pin this entire defensive drop off on the absence of Swanson? 

The void that Swanson leaves at shortstop isn’t felt quite as acutely as the downstream effects are. The Cubs were fifth in FRV from their shortstops prior to Swanson going down, and in the month since, they only dropped to eighth. It’s the slide of Nico Hoerner from second base to short that really hurts. Pedro Ramírez has had a fine rookie season, and he filled in admirably in Hoerner’s stead, but the Cubs went from eighth in FRV at second base when Hoerner was the primary player at the keystone, all the way down to 18th with Ramírez as the primary guy.

One way we can attempt to further isolate this is by seeing how often the Cubs defense turned groundballs into outs. According to FanGraphs, the Cubs allowed a .219 batting average on groundballs with Swanson in the fold, and that jumped to .229 in the month that he was on the injured list. That doesn't capture the value that also leaked away due to more errors (Hoerner committed three while playing shortstop; Swanson has only committed seven in about five times the playing time) or due to double plays not being turned, but it gives us some inkling.

Defense is really hard to measure, especially in such small sample sizes, but I come away from this with two takeaways:

1. The Cubs should be very grateful to have Nico Hoerner. He accepted his shift to second base four years ago without blinking. The shift from the left side of the infield to the right side is something we’ve seen lesser shortstops create drama over. Not this one, and as a result, the Cubs have essentially a shortstop at each middle infield position. When one goes down, the other can move over. 
2. The Cubs should also be extremely glad to have Dansby Swanson back. There was a noticeable decline in how this group graded out without their shortstop. It might feel marginal, and it is. However, playoff games are won on the margins. 

Their pitching depth is still in doubt, and they might yet have to play the Wild Card Series on the road. Positionally, though, the Cubs are back to full strength, and the difference between being without Swanson and having him back can't be overstated.

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