As we talked about last night, pitcher replacement level is set at a .380 win% for starters and .470 win% for relievers. However, because of the differences between the AL and the NL, as well as varying offensive levels over the years, that means that there isn’t a fixed mark that we can point to as replacement level FIP that works for each year and each role.

However, since we’ve got the .380/.470 marks, we can derive those numbers with just a little bit of work. Let’s walk through the process, first using a 2008 American League starting pitcher as our example.

The league average runs per game in the AL last year was 4.78. The FIPs that are displayed on the pitcher’s player card here at FanGraphs are scaled to ERA, but for the win values, we modified the formula slightly to scale it to match league RA. However, there’s a shortcut if you want to take a pitcher’s traditional FIP and have it match up with the league RA – that’s dividing his FIP by .92.

For instance, a 4.40 FIP divided by .92 will give you a 4.78 FIP. That .92 is the ERA-RA bridge, and allows us to conclude that 4.40 would be a league average FIP in the American League last year. So, a pitcher with a 4.40 FIP in a neutral park would be a league average pitcher. Or, put back into win% terms, a .500 pitcher.

Now, because we’ve set replacement level at .470 for relievers and .380 for starters, we know that a replacement level FIP for an AL reliever will be a lot closer to 4.40 than it will be for a starter. How much closer? Running the numbers through the formula gives us a 4.68 FIP (traditional, not scaled to RA) for an AL reliever and 5.63 for an AL starter. So, if you’re looking at a pitcher’s FIP here on his FanGraphs page, and that pitcher happens to be in the American League, those are the numbers you’d want to compare him to in order to see how far away from replacement level he is.

For the NL in 2008, the numbers are 4.45 for a reliever and 5.37 for a starter – the lack of a DH drives down the league’s offensive level, and so the performance of a replacement level pitcher will appear better in the NL than in the AL.

Remember, these are park neutral numbers, so if you’re looking at a player who pitched in a park that significantly effects offense, you’ll have to adjust his FIP to account for the park effects. If the NL starter that we were looking at pitched in a park that suppressed offense by 5%, then a replacement level for that park would be 5.10, not 5.37. Thus, you’d want to use the lower replacement level for his home innings, and the league average replacement level for his road innings. Assuming equal distribution, that would make the replacement level FIP 5.23 for that NL starter pitching in a park with a park factor of .95.

As you can see, the run environment that the pitcher exists in has a substantial effect on the replacement level value. But the impact of run environments don’t stop there, and are further complicated by the fact that starting pitchers have a significant impact on their own run environment. The expected offensive level is a lot lower in a game where Johan Santana is pitching than where Cha Seung Baek is pitching. In order to calculate the runs to wins conversion for each pitcher, we have to take into account that a pitcher impacts his own run environment. We’ll talk more about this later this afternoon.