Quick Study: The Effect of Defense on a Low-Strikeout Staff
The Royals outperformed their preseason projections here at FanGraphs by a substantial 16 wins. The Royals also assembled one of the best defensive teams in the majors this year — and have done so for much of the recent past. Indeed, from 2011 to 2015, the Royals have produced the league’s highest UZR total (175), averaging 35 runs saved per season above average.
One area I have not seen quantified is the effect a good defense (such as that possessed by the Royals) might have when combined with a low-strikeout pitching staff. Would a good defensive team’s pitchers and defense record more outs and post lower ERAs than FIPs? Probably some, but also how much of difference would it actually make? I decided to perform a quick study to see if there was anything to my little theory.
Here’s what I did:
- Looked at all teams from 2005 to 2015.
- Grouped the teams that were one standard deviation (~5 UZR/150) from the average UZR/150 into two groups, Good and Bad. Also, divided the average group into those with positive and negative defensive values to make four groups.
- In each of four groups, divided them further into teams with above average strikeout rates (7.0 K/9 was the delimiter) and below average ones.
- Finally, averaged each of the eight groups’ ERA-FIP. Also: calculated the difference in the values along with the number of runs saved over the course of a season.
Here are the values:
| Defense Rating | High K | Low K | Diff | Total Runs Saved |
| Good | -0.192 | -0.222 | -0.030 | 4.9 |
| Above Average | -0.068 | -0.125 | -0.057 | 9.2 |
| Below Average | 0.062 | 0.097 | 0.035 | -5.7 |
| Bad | 0.208 | 0.243 | 0.035 | -5.7 |
Well, there is a difference in ERA-FIP for the high and low strikeout teams, but the difference doesn’t widen in this simple example. In all, a team seems to get about five extra runs saved (or about half a win) by having an above average defense when the pitching staff’s strikeout rate is below average. Not a huge difference, but some.
Jeff, one of the authors of the fantasy baseball guide,The Process, writes for RotoGraphs, The Hardball Times, Rotowire, Baseball America, and BaseballHQ. He has been nominated for two SABR Analytics Research Award for Contemporary Analysis and won it in 2013 in tandem with Bill Petti. He has won four FSWA Awards including on for his Mining the News series. He's won Tout Wars three times, LABR twice, and got his first NFBC Main Event win in 2021. Follow him on Twitter @jeffwzimmerman.
The problem with this is that it assumes that FIP is a perfect estimation of a team’s pitching independent of a defense. It’s not.
In fact, a lot of high strikeout pitching staffs are adept at inducing pop ups, which might explain why there isn’t much of an observed difference here.
In other words, high strikeout staffs might outperform their FIP anyways, while low strikeout staffs might underperform their FIP, simply because the high strikeout skill set tends to correspond with more pop ups.