The most famous number on a pitcher's stat line is earned run average, or ERA. It tells you how many earned runs a pitcher allows per nine innings. But reading a pitcher by ERA alone means seeing only half the picture. Runs allowed are a result, and other stats show the process behind that result.
For starting pitchers, an ERA in the 2s is ace territory. The usual rule of thumb reads the 3s as a very good starter, the 4s as a pitcher holding down a rotation spot, and 5 or higher as a pitcher whose spot is in danger. These lines move up and down, though, with whether the league as a whole favors hitters or pitchers. In a hitters' era, an ERA in the low 4s is a solid result. In a pitchers' era, an ERA in the 3s becomes ordinary.
WHIP is the number of runners a pitcher allows per inning: hits plus walks, divided by innings pitched. If ERA is the result, WHIP is the process. A pitcher who puts few runners on base never creates the situations where runs score.
| WHIP | What it means |
|---|---|
| 1.10 or lower | Top of the league. Trouble itself is rare |
| 1.20s | A steady rotation starter |
| 1.40s | Pitching with runners on base every inning |
| 1.50 or higher | Runs are only a matter of time |
A pitcher with a good ERA but a bad WHIP is likely just barely escaping jams, and that kind of luck usually does not last. On the other hand, a pitcher with a good WHIP but a high ERA has probably just had a few bad breaks pile up, and has a good chance to bounce back.
It is not flashy, but eating innings is the skill clubs value most. When a starter lasts six or seven innings, the bullpen gets rest, and a rested bullpen changes the whole team's month. A starter who throws 170 or more innings in a season is a pillar of the team in his own right. Power pitchers who rack up strikeouts get the spotlight, but pitchers who go deep into games hold the team up.
The same stat has to be read differently depending on a pitcher's role. A closer throws only about 60 innings a season, so the ERA sample is small and the number swings with one or two games. That is why save conversion rate and WHIP give a more accurate view of a closer. For relievers, contributions and mistakes that don't show up in earned runs, such as inherited runners who come around to score, make the context outside the numbers even more important. In the end, the grammar of pitching stats comes down to one rule: put result stats and process stats side by side, and read them with the pitcher's role and environment in mind.
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