Obviously I can't resist doing a Prospect Retrospective for him. It is pretty easy one to write.
Prior grew up in California, but went to Vanderbilt for his freshman season in 1999. He went 4-8 with a 4.59 ERA in 13 starts, with a 71/23 K/BB in 82 innings. That wasn't horrible for a college freshman, but it prompted a move closer to home: he transferred to the University of Southern California for 2000. He thrived, going 10-6, 3.49 with a 143/43 K/BB in 129 innings as a sophomore, then really took off with a 15-1, 1.70 ERA with a 202/18 K/BB in 138 innings as a junior.
He was widely regarded as the best player available in the 2001 draft, but he went second-overall to the Chicago Cubs after the Minnesota Twins went with hometown boy Joe Mauer with the first slot.
Prior was considered one of the very best college pitchers in history, mentioned in the same breath with Tom Seaver, and the closest thing you can be to a "can't miss" prospect. Still, my inherent conservatism caused me to give him "just" a Grade A- entering 2002, writing that he should be a good pitcher at the very least and "possibly a great one," but also noting the mixed recent history of other "best college pitchers" like Paul Wilson and Ben McDonald.
Prior moved fast. He began his pro career in Double-A, going 4-1, 2.60 with a 55/10 K/BB in 35 innings. Promoted to Triple-A Iowa, he posted a 1.65 ERA with a 24/8 K/BB in 16 innings over three starts. That got him to Wrigley Field quickly, and he had no problems at all adapting to the major leagues: he posted a 3.32 ERA with a 147/38 K/BB in 117 innings with 98 hits allowed, a 3.16 FIP, and a 2.8 WAR. He was already an excellent major league pitcher.
And you know the rest of the story.
He was outstanding in 2003: 18-6, 2.43 ERA, 2.47 FIP, 245/50 K/BB in 211 innings, 183 hits, 7.6 WAR. He did miss three weeks after a collision with Marcus Giles. And of course you know how Dusty Baker rode Prior hard down the stretch and in the post-season. Prior was big, strong, young, threw hard, threw strikes, and had (what was considered at the time) to be good mechanics.
Then the injuries started. Achilles tendon in 2004. Sore elbow in 2005. Shoulder and oblique problems. He was still very effective when he took the mound, posting a 2.7 WAR in 2004 and a 3.0 in 2005. But could he actually stay healthy long-term?
In the spring of 2006 I wrote a "Young Pitcher Symposium" article about Prior, summarizing his career to that point and looking at his comparable pitchers to that stage in his career using Sim Scores and PECOTA comps.
Here is what I came up with: remember, these were the comps I came up with in the spring of 2006.
Don Wilson: 1748 innings over 9 seasons, career over at age 29. Career record 104-92, ERA+109. A comparison with Prior may be misleading, since Wilson's career ended because he died.
Erik Hanson: 1555 innings over 11 seasons, career over at age 33. Career record 89-84, ERA+106. A very strong pitcher when healthy, but he had injury problems for several years and was no longer effective after age 30.
Stan Williams: 1764 innings over 14 seasons, career over at 35. Career record 109-94, ERA+108. Very effective early in his career, overpowering at times, but was injured and on the shelf most of the time from age 26 through 30.
Scott Sanderson: 2562 innings over 19 seasons, career over at 39. Career record 163-143, ERA+102.. Threw hard early in his career, but injuries sapped his velocity, forcing him to rely on movement and control. Frequently injured from age 26 through 32, though usually pitched well when not hurt.
Bob Welch: 3092 innings over 17 seasons, career over at 37. Career record 211-146, ERA+ 106. Injuries and personal problems cost him time in his early 20s, but he had a solid run of pitching in his early 30s.
Steve Busby: 1061 innings over 8 seasons, career over at 30. Career record 70-54, ERA+ 105. Brilliant pitcher in his early 20s, but burned his arm out quickly.
Mario Soto: 1730 innings over 12 seasons, career over at 32. Career record 100-92, ERA+108. One of the best pitchers in the game for three seasons, 1982 through 1985, but his arm blew out.
Ramon Martinez: 1896 innings over 14 seasons, career over at 33. Career record 135-88, ERA+ 105.Outstanding early, hurt his arm at age 24 and was never really the same afterward, though he held on as an adequate starter for some time.
Based on the historical precedents, my thinking was that Prior would never fully live up to his early potential, but that he would end up having a solid overall-career, perhaps dragging things out like Scott Sanderson, whose arm was held together by duct tape and spit but who kept on pitching.
Alas, Prior's arm problems were more than even modern sports medicine could handle. Of the comps heading into 2006, the one he ended up closest to was Steve Busby, famous Kansas City Royals pitching burnout from the 70s.
So was it all Dusty Baker's fault? Well I'm sure the way Prior was used in 2003 was part of the problem, but I don't see how it can all be laid on Dusty. As I wrote in 2006:
It should be noted that Prior was a California high school pitcher and a California college pitcher: he has more mileage on his arm than a lot of pitchers his age. "Flawless" mechanics or not, his health problems have not been out-of-bounds from what you'd expect given his background
And of course, in retrospect Prior's mechanics were not flawless, at least if you buy into theories about "Inverted W" arm action and excess scapular loading.
In any event, Prior was a really good pitcher for a brief period of time: 42-29 (.592), 3.51 ERA in 657 innings, 757/223 K/BB, 124 ERA+, WAR 15.8. It could have been so much more, but the same can be said for a few dozen other guys who burned out too fast.