ERA — The Headline
Earned Run Average measures earned runs allowed per nine innings. A 2.50 ERA is excellent; 3.50 is league average; above 4.50 is below average. ERA is luck-soaked: it depends heavily on the fielders behind the pitcher and on the timing of the hits he allows.
WHIP — The Traffic Meter
Walks plus Hits per Inning Pitched. Around 1.10 is excellent, 1.30 is average, 1.50 is trouble. WHIP is steadier than ERA because it ignores the run-scoring sequence, but it is still influenced by the defence behind the pitcher.
FIP — The Truth
Fielding Independent Pitching is built only from outcomes the pitcher fully controls: strikeouts, walks, hit-by-pitches, and home runs. By construction it strips out luck and defence. A pitcher carrying a 3.10 FIP and a 4.40 ERA is being unlucky and should improve as the sample grows; the reverse is the trap most casual analysts fall into.
How Ra Uses Them
The model weights FIP and Statcast-derived expected stats first, then ERA, adjusted for park and recent form. Together they answer the only question that matters: what is this pitcher’s true skill, and what should we expect from him tonight?