When you’re at a ballgame, drinking a Golden Road Mango Cart whilst eating a hotdog or cheesesteak, you might end up looking at the various metrics on the scoreboard: batting average, slugging, on base percentage, OPS, strikeouts, pitch speed, ERA, etc. The penultimate is what we will examine in this article, specifically on why it’s not accurate in measuring pitching skill. So the next time you see a pitcher with a 4.30 ERA, it’s best not to assume that the pitcher is inadequate.
What is ERA?
ERA stands for earned runs average, and we must understand what earned runs are before talking about ERA.
According to the MLB glossary, an earned run is…
“…any run that scores against a pitcher without the benefit of an error or a passed ball”
This means that any run that a pitcher gives up will be counted as an earned run for the pitcher. It sounds a bit contradictory, because an earned run sounds like it is in favor of the pitcher, due to the positive connotations of earned; it is not, more earned runs means a pitcher is giving up more runs to the opposing team. This leads us to ERA, which is…
“…number of earned runs over 9 innings”
With a formula,
ERA = 9*ER/IP where IP is innings pitched
If we increase ER, then ERA goes up; if we decrease ER, then ERA goes down. You can’t really talk about manipulating IP, because a pitcher’s IP will always go up whenever you pitch, so it’s best to think of it as something that cannot be changed, or a constant (as applied mathematicians like to call it).
We now have a general idea behind ERA, and how that may define a great or poor pitcher; the higher the ERA the worse the pitcher and vice versa. There is a flaw to solely using ERA as a metric for evaluating pitcher skill, and it lies within the intricacies of what an ER is.
Behind an Earned Run
Once again, an earned run is simply…
“…any run that scores against a pitcher without the benefit of an error or a passed ball”
This doesn’t necessarily mean a home run by the hitter; it also includes RBI (runs batted in) raked in by the opposing team. This means that if a flyball goes to left field, ball clear as day, and the left fielder fails to catch it, it is most likely going to count as an earned run for the pitcher. Basically, a poor defense can drastically increase a pitcher’s ERA when the increase in ER is not the pitcher’s fault. Likewise, a great defense can potentially decrease the amount of earned runs a pitcher acquires, which also isn’t indicative of pitcher skill. With this being said,
ERA is a good indicator of how many runs are given up by the defense with that particular pitcher, but not necessarily pitching skill. This leads us to the big question, what properly evaluates pitching skill?
Intro to FIP
FIP stands for fielding independent pitching, and by looking at its name, it begins to alleviate the exact problem we have with ERA.
According to the MLB glossary, FIP is…
“FIP is similar to ERA, but it focuses solely on the events a pitcher has the most control over -- strikeouts, unintentional walks, hit-by-pitches and home runs. It entirely removes results on balls hit into the field of play”
It makes a lot more sense to gauge a pitcher’s skill over what they have control over, rather than to have partiality due to a poor or great defense. When we look at the equation it becomes more clear when we talk about ‘events a pitcher has the most control over’…
FIP = ((HR x 13) + (3 x (BB + HBP)) - (2 x K)) / IP + C where C is the FIP constant.
We see here the weights for each respective event a pitcher has control over. Pitchers have control over home runs, balls (unintentional) and hit by pitches, and strikeouts. As we can see in the equation, there is no consideration of batted balls in play. The FIP constant is a constant determined by the MLB each year to scale it to ERA, so we can interpret FIP on the same scale of ERA.
Weights
In mathematical lingo, we say that FIP is a linear combination of HR/IP, BB/IP, HBP/IP, K/IP; to a layman this means that each event is weighted by a number/IP. For example, home runs are weighted by 13/IP, BB are weighted by 3/IP, and so on… It makes sense that FIP has a greater penalty on home runs because this could harm the pitcher the most in the form of a grand slam.
Notice that the weight of strikeouts are, -2/IP. The negative is odd, but makes a lot of sense because the more strikeouts a pitcher gets, the lower FIP the pitcher has, meaning the pitcher is more skilled at controlling events within their power. Basically, more strikes outs equals a better pitcher, and this makes sense to anyone who’s watched baseball.
Final Thoughts
Yes, FIP is a great step in evaluating pitching skill, however, there are a few flaws with it. There can potentially be a line drive that is physically impossible for a fielder to receive, and the pitcher would be at fault for this. This is one example of a batted ball in play that can be at the pitcher’s fault, and the way to alleviate this can be through including more batted ball data into the FIP equation.
There are other metrics like SIERA and xFIP that are better than evaluating pitchers than FIP, but FIP is definitely the simplest modern metric to grasp, and the perfect place to look at a detailed and more fair evaluation of pitching.
Notes
More detailed reading on FIP,
Further reading on SIERA