Replacement Level Pitching Part II
In part one of this, I talked about why we compare players versus the baseline of a replacement player instead of a bench player. Then, I showed what a sub-replacement level pitcher looks like in Kei Igawa, and gave an example of a replacement level pitcher in Sidney Ponson, who fits the definition perfectly. Now we’ll get on with the rest of it, talking about how to value pitchers in differing roles and situations, like Joba Chamberlain, Chien Ming Wang, and Andy Pettitte.
Andy Pettitte threw 204 innings with a 4.54 ERA this past season. Chien Ming Wang threw only 95 innings in an injury-shortened season, putting up a 4.07 ERA. Wang was better, but pitched in fewer innings, so who was more valuable to the Yankees? The same question can be asked about Joba Chamberlain and Mike Mussina. If you remember from part one, I said that replacement level for relievers is lower than it is for starters. So we also need to look at the time Joba spent in the bullpen, and also account for the fact that the 8th inning is more important than the first inning before saying how valuable he was. It might sound a little complicated, but I promise you it’s not, once it’s all spelled out in plain English. More after the jump…
The full-time starter: Andy Pettitte
Andy Pettitte’s 2008 was decidedly average. His 4.54 ERA was slightly below league average, but other stats like strikeout to walk ratio were above average. Some people might say that Pettitte hurt the Yankees last year with his performance. “If he wasn’t above average then how could he be helping?” So how about we compare him to a replacement level pitcher (or as we saw in part one, Sidney Ponson). There are two things to remember here: 1) replacement level starter is projected to have a 5.50 ERA, and 2) that starter will not be projected to throw more than 160 innings, since a pitcher that bad wouldn’t be allowed to throw that many innings. But Pettitte threw 204 innings last season, so we fill in the remaining 44 innings with the relief replacement level ERA of 4.50. So in 204 innings of replacement level pitching (starter and relief combined), the tandem would give up about 120 runs (98 from the starter, 22 from the reliever). Pettitte, in those 204 innings, gave up 103 runs. The difference between the two numbers is 17 runs, and that is the value that Pettitte provided above what replacement level pitchers would provide in equal playing time.
The injury-shortened season: Chien Ming Wang
So we see that Pettitte was worth 17 runs above replacement last season, but Wang pitched better in the time that he was on the mound. In 95 innings out of the starting rotation, Wang put up a 4.07 ERA, allowing 43 runs. A replacement level starter would have allowed about 53 runs in the same amount of time. By taking the difference, we see that Wang was worth 10 runs above replacement last season. There’s nothing groundbreaking in this paragraph, I just wanted to get the answer to my Wang/Pettitte question from before.
The next section will be a little more cumbersome.
The Swingman: Joba Chamberlain
While not a swingman in the truest sense of the word (and it’s not even a word according to spell check), Joba Chamberlain shuffled back and forth between the bullpen and rotation last season. As we saw with Andy Pettitte above, there is a different baseline for relievers than for starters. So first, we must compare Joba’s numbers as a starter to replacement level, and get a value for that. Then, we take his relief numbers and compare those to the 4.50 baseline. But the later innings have a greater importance than the innings before them, and we must account for that. Luckily, there is a stat called Leverage Index that does just that.
As a starter, Joba threw 65 and 1/3 innings with a 2.76 ERA, giving up 20 earned runs. A replacement level starter would be expected to give up 36 runs in that span, so Joba was worth 16 runs above replacement as a starter. That’s in just over 65 innings. Wow. Hold on to that “16 runs” for later when we add this up.
As a reliever, it’s more complicated. The first part is still the same… compare his 2.31 ERA in 35 innings to the 4.50 replacement level, and get an 8.5 run difference (9 runs in 35 innings, subtracted from 17.5 rep. level. runs gets 8.5). Now, we account for leverage. If you don’t know what Leverage Index is, you can read a basic introduction here. Chamberlain’s LI while in relief last season was 1.35. To adjust his value above replacement (9 runs in relief) to account for this, we take the half-way point between 1.35 and 1.0 (1.175), and multiply them together. This comes out to 1.175 x 8.5 runs = 10 runs above replacement, accounting for leverage. Add the starter and relief versions of Joba Chamberlain together, and you get 26 runs above replacement.