This is a topical piece sent to me by Steve Nelson, formerly of Mariners Wheelhouse, reprinted here in its entirety:
Felix Hernandez is forcing a discussion about whether he should be added to the big league roster. It's a good guess that Hernandez would be more productive on the Mariners' MLB roster than whatever pitcher would be bumped to make room for him. So most of the considerations about whether to add him to the major league roster focus on whether it's detrimental to a pitcher's development to be promoted at an early age. The concerns include presumed greater injury risk and questions of mental makeup and emotional maturity. As regards the Mariners, they certainly have proven themselves at least as adept at blowing out arms in the minors as they have in the majors - maybe even more adept since the largest portion of their debilitating arm injuries have occurred while players were still in the minors. So I don't see any logic at all in the notion that sending Hernandez to the minors is somehow going to protect him from injury.
The assumption is that not promoting teenagers to MLB even though they are physically and emotionally ready will give them longer and more productive MLB careers. So let's consider if there are data to support the assumption that keeping a young player in minor league ball simply because he is young and after he is ready to contribute effectively at the MLB level is detrimental to his career. In the discussions I have seen to date on this issue, no one has produced any hard data to support the assumption that early promotion is a bad idea. Most commentators simply cite anecdotes, most of them involving Doc Gooden. But for every Doc Gooden example that can be cited, there is at least one offsetting Bob Feller type of example that can be cited. If anyone has data that says that keeping pitchers in minor league ball after they are capable of pitching on a major league roster, please give a link or source in the comments area. Note also that guys like David Clyde don't belong in this discussion, because Clyde made his debut as a Charlie Finley promotional gimmick when he had not shown at all that he was ready to pitch in MLB.
Since we need more than anecdotal information here, about a month ago I did some more systematic investigation of this issue. I figured that if promoting pitchers while they were young was bad for their careers, those young pitchers should have shorter careers than other players. I normally use 100 IP as the criteria to identify a pitcher who has enough value for a team to continue giving him the ball regularly during a season. If a pitcher is not good enough overall to justify 100 innings of use, he's either going to be relegated to a fringe situational usage role (e.g., a LOOGY) or be dropped off the roster. So, running some queries on Sean Lahman's excellent database at The Baseball Archive, I created a spreadsheet that listed every pitcher that had a major league debut after 1900 and that had at least one 100-inning season during his career. The spreadsheet gave me age at MLB debut and number of seasons in which they pitched more than 100 innings.
So if bringing young studs to the majors is detrimental to their health, we should see them having shorter careers, and this should show up as logging fewer seasons with more than 100 IP during their career as compared with the overall group of pitchers who are good enough to reach the majors and log at least one 100-IP season during their career.
I expected the data to show clearly that early promotion was bad idea. When I put the information together that was not what I found. The results of the comparison are shown below:
Frankly, I don't see a whole lot of difference between the groups. The one thing that stands out is that pitchers who debut at an early age and log at least one 100-IP season are far more likely to have at least two 100-IP seasons than the larger population of pitchers. I suspect that's not a health issue; it's more likely that a guy who debuts at an early age is unlikely to be a guy who gets one and only one chance to make a mark in the big leagues.
Also, pitchers who debut at an early age are more likely to provide seven or more seasons of productive performance. That makes sense, since those pitchers are likely to be more talented than the overall population of pitchers. But if early promotion was a horrendously bad idea, then the young studs should have washed out - a la Doc Gooden - before being able to log that many productive seasons.
BTW - it's hard to parse the data for younger debut ages because you start to get to small sample size effects. But there are still many individual cases of pitchers who debuted as teenagers in the modern era and were extremely effective pitchers for many years. Specific examples (with age at Major League debut indicated in parentheses) include Bob Feller (17 years old), Joe Nuxhall (15 years old), Claude Osteen (18 years old), Larry Dierker (18 years old), Lew Krausse (18 years old), Milt Pappas (18 years old), Herb Pennock (18 years old), Hal Newhouse (18 years old), Curt Simmons (18 years old), Chief Bender (18 years old), Catfish Hunter (19 years old), Bert Blyleven (19 years old), Ray Sadecki (19 years old), Babe Ruth (19 years old), Sandy Koufax (19 years old), Jim Palmer (19 years old), Nolan Ryan, (19 years old), Early Wynn (19 years old), Wilbur Wood (19 years old), Don Drysdale (19 years old), and Walter Johnson (19 years old). Looking at that list of talent, I think it's hard to categorically say that keeping a guy in the minor leagues when he's MLB ready is bad for his career.
So that's it. I know of no data to support the notion that keeping a player in the minors shortens his career. There is no reason to believe that a pitcher is somehow more protected from injury in the minors than in the majors. To the contrary, the slim data I assembled here suggest that promoting players when they are ready to contribute does not affect the number of productive seasons likely to be produced by that pitcher. And for every example that can be cited of a player who may have been harmed by early promotion, there are several examples of players who clearly were not harmed by that promotion. And that is even granting the unprovable (and improbable) assumption that flame-out guys such as Doc Gooden wouldn't have succumbed to their same demons had they stayed in the minors an extra season or two.
If Felix Hernandez is physically ready to contribute at the MLB level and the team decides he is emotionally ready to pitch at the MLB level, there is no reason to keep him in the minor leagues thinking that will protect his health or prolong his career.