Sunday, February 25, 2007

Jake Peavy’s Off Year

If I had to pick one thing that prevents the casual fan from truly understanding baseball, I would say it’s the continued existence of the stat BA (batting average). Coming in second place would be the continued prevalence of ERA as an important stat. In a fairly recent espn.com pole OPS was actually cited very highly in a list of most looked at baseball statistics, a refreshing development indeed. However, for pitching stats, ERA was still listed as the one looked at most for evaluating a pitcher’s performance. Earned Run Average is a more indicative stat than Batting Average (assuming an appropriate sample size for both), but it’s still pretty poor. It’s especially not good because people judge pitcher’s solely on that stat, labeling them a bust or success based on their final ERA.

Beyond all of the luck involved, pitchers can even (to some extent) fake their ERA, which can’t be said for BA. For instance, among average starters, ERA is tied somewhat to innings pitched. A pitcher averaging less innings due to a strong bullpen/arm concerns/etc can achieve a lower ERA by not having to go through the same lineup as many times, whereas the horse of the staff may end up giving up a substantial number of 7th or 8th inning runs. That’s one of the reasons Jaret Wright can keep his ERA below 6, he’s never allowed to face hitters a 4th time. Conversely Curt Schilling, a guy whose job description includes eating up innings to save the bullpen, over the last 3 years has allowed a 717 OPS in his first 90 pitches but allowed a 829 OPS from pitches 91 to 135. His ERA takes a hit for working those extra innings. His strikeouts per 100 batters faced (a better indicator of pitching ability) stays very constant however, at 23K (per 100 BA) over his first 90 pitchers and actually rising to 25K (per 100 BA) over his final pitches.

The point of all this is that really a few mistakes or misadventures during the year can really affect one’s ERA severely, while other indicators like SO/9, WHIP, etc. more precisely set the bar for one’s expected pitching production. Those are the stats to look at together to form a complete picture of a pitcher’s ability. A stat like 3 run home runs allowed will greatly affect ERA while not affecting WHIP nearly as much. Further, a guy allowing a lot of home runs one year will not necessarily be so home run prone the next year, unless many other of his stats also reflect the fact that he’s getting hit hard often.

These considerations should mean everything for people drafting for fantasy leagues when it comes to ranking Jake Peavy. His ERA of 4.09 last year stands out after finishing at 2.27 and 2.88 in 2004 and 2005 respectively. As does his Won-Loss in 2006 (11-14) compared to 15-6 in 2004 and 13-7 in 2005. Look at K/9 through those three years though: 9.36, 9.58, 9.56. And BB/9: 2.87, 2.22, 2.76. And WHIP: 1.20, 1.04, 1.23. If anything, the main difference between 2006 from the other years was that he was allowing more balls hit in play to be hits, and more runners who reached base ended up scoring, 2 factors that aren’t necessarily greatly a reflection of a pitcher’s ability. Even after getting hit a little harder than you would expect in 2006, Peavy still finished 1st in MLB in K/9 (in front of Johan Santana and Carlos Zambrano) and 16th in WHIP, above many other aces. Barring unforeseen arm troubles I would expect him to be right near the top of all MLB pitching stats in 2007, with an ERA in the mid 2s in the NL West. It will be seen as a great bounce-back season by many, but actually will merely be a statistical regression to the mean of excellent ability.

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3 Comments:

Anonymous Anonymous said...

lame. the guy's pitching in the weakest hitting division in baseball, and he can't keep his era under 4? overrated!

4:24 PM  
Blogger alex said...

Wow, someone actually reads this stuff! Awesome.

9:46 PM  
Anonymous Kyria said...

Thanks for writing this.

9:33 AM  

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