How the Same Defense Helps One Pitcher and Hurts Another

Freddy Peralta is having arguably the greatest season of his excellent eight-year career. The right-hander has ridden a career-best 2.69 ERA to a career-high 16 wins. However, I used the word arguably for a reason. Peralta’s 3.64 FIP is just the fourth best of his career, and his 3.93 xFIP is tied with 2024 for his fifth best. There’s a gap of 0.95 runs per nine innings between his FIP and his ERA. When you multiply that times his actual innings total of 163 2/3, FIP thinks he should’ve given up just over 17 more earned runs than he actually has allowed. None of this is surprising. Pitchers underperform or overperform their peripherals all the time. The interesting thing is that Statcast says that no pitcher has benefitted as much from the defense behind him as Peralta. When he’s has been on the mound, the Brewers defense has been worth just under 14 fielding runs. It’s neither this simple or this clean-cut, but it’s easy to combine these two numbers and make an inference: Defense can explain more than 80% of the difference between Peralta’s FIP and ERA.
On the other end of the spectrum is Peralta’s teammate Brandon Woodruff, who returned from shoulder surgery in July and has gone 6-2 over 11 starts and 59 2/3 innings. He’s posted a 3.32 ERA, 3.26 FIP, and 3.40 xFIP. In other words, FIP thinks Woodruff has gotten exactly what he’s deserved. However, Woodruff’s xERA is a scant 2.27. When you combine all those numbers, it means Statcast thinks several batted balls that should have resulted in outs instead fell in for non-homer base hits. The difference is a bit over six runs. Coincidentally or not, Statcast says the Milwaukee defense has been at its worst behind Woodruff, costing him just under five runs, once again just about 80% of the gap between an ERA estimator and his actual ERA.
That’s why we’re talking about Peralta and Woodruff. No two teammates have a bigger gap between the fielding run value of the defense behind them. It’s nearly an 18-run gap! It’s jarring. With 26 FRV, Statcast thinks the Brewers have the fourth-best team defense in the game, but somehow none of that brilliance has been shining on Woodruff. We’re going to use Statcast data to break down, as best we can, the reasons behind it. Hopefully, the comparison will show the various ways a team can provide defensive value. Let’s start with the catching numbers. Read the rest of this entry »









