Danny Salazar and baseball's elite, young strikeout pitchers

Danny Salazar started the home opener on Friday. He wasn't at his best, but managed to get through 5.2 innings while allowing only 2 runs to score. In some ways what stood out is that he recorded only 4 strikeouts. In 10 starts last year he struck out so few only twice. Salazar has been a strikeout machine so far in his young career. In fact he posted the highest strikeout rate by a 23-year-old starting pitcher in MLB history (minimim of 50 IP). Salazar whiffed 11.25 hitters per 9 innings last season; in addition to being the highest rate by a 23-year-old starter, it's also the highest rate ever by an Indians starter of any age.

A lot is riding on Salazar's ability to continue developing into a good pitcher. He's generally viewed as the Indians' #2 starter now, and with Justin Masterson in his final season before free agency, the rotation is likely to look very, very shaky a year from now if Salazar doesn't have a strong year.

There are a number of different ways you could collect comparison points for Salazar, and I think age and strikeout rate are among the more reasonable ones, so I tracked down every pitcher in MLB history who pitched at least 50 innings as a starter in their age-23 season and struck out at least 9 per 9 innings. It turns out there have been 23 pitchers who fit that description. That number includes Salazar, as well as Tony Cingrani (10.32) of the Reds and Sonny Gray (9.42) of the Athletics, all of whom joined the list in 2013.

13 of those 23 seasons have come since 2007, as strikeouts are at an all-time high these days.

What I'm interested in is seeing how these guys did when they were 24 and older, so here are the 20 guys who joined the list prior to last season (including a pair of the best young pitcher in Tribe history), with their age-23 and age-24 numbers. I've also included a few other measures that I think tell us a fair amount about how well a pitcher has done (for reference, Salazar's BB/9 was 2.60, his HR/9 was 1.21, and his ERA+ was 121).

17 of those 20 pitchers started 25+ games in their age-24 season, with the exceptions being Herb Score (his age-24 season is when he was struck in the face by a line drive), J.R. Richard (who spent most of that year in the minors), and Jordan Zimmermann (who missed most of that year due to Tommy John surgery).

Only 4 of the 20 saw an increase in their strikeout rate, which is to be expected, because outliers are almost always more likely to regress to the mean than get further from it. 11 of them were still at 9+ per 9 innings, and 16 of them were at 8+. 11 of the 20 saw an improvement in their walk rate in their age-24 season, while only 8 saw an improvement in their home run rate, and only 7 saw an improvement in their ERA+ (while 2 posted an identical number).

Mean and median changes in K/9: -0.82; -0.71

Mean and median changes in BB/9: -0.32; -0.15

Mean and median changes in HR/9: +0.02; +0.06

Mean and median changes in ERA+: -8; -4

There's all kinds of fluctuation in those numbers, but on the whole, that group of pitchers was similar at age 24 to what they'd been at age 23, but just a little bit worse. We shouldn't expect Salazar to strike out 11.25 per 9 innings again, but 9+ seems a reasonable target, and 10+ is certainly possible, and reaching either of those benchmarks would likely mean he'd put up a year Tribe fans would be happy with.