SwStk% and K/9

The SwStk% metric is one of my favorites on FanGraphs. We would expect the statistic to be a good proxy for a pitcher’s raw stuff, as a swinging strike is the ultimate pitch result. Therefore, it should correlate highly with strikeout rate. And intuitively, it does. From 2001-2010 using a sample size of 59 pitchers, SwStk% had a 0.87 correlation with K/9. It is not higher because luck still plays a role, and K/9 includes called strikes which obviously SwStk% does not. So now that we know SwStk% matches up with K/9 quite well, I like to rank pitchers by each to determine who might have some hidden strikeout rate upside or downside.

I looked at 92 pitchers from 2010 and compared how they ranked in SwStk% and K/9. A better ranking in K/9 than SwStk% indicates potential downside, while a better ranking in SwStk% would suggest potential upside.

First, I present the 10 pitchers with the largest difference in the two metrics where the ranking in SwStk% is better than K/9. These are the upside guys.

Clay Buchholz stands out near the top of this table. While the majority of fantasy owners rightfully expected some major ERA regression in 2011, I personally did not believe that regression would lead as high as his 2010 xFIP of 4.07. The scouting of his stuff supports his strong SwStk% so I think he has significant K/9 upside, which should offset some of the luck neutralization this year. Hiroki Kuroda‘s SwStrk% has never been below 9.2, yet his K/9 has never matched up with these strong marks. Kuroda is always undervalued in fantasy leagues to begin with so the possible promise of a higher strikeout rate is even more of a reason to get excited. If only Jaime Garcia’s innings jump did not scare me away, he would be one of the more intriguing pitchers for this season, given his strikeout and ground ball combination. Shaun Marcum could be a darkhorse Cy Young candidate after his move into the National League, but his past injury issues, including this spring training, caused me to shy away. If Johnny Cueto can return fully healthy and his increased ground ball rate in the second half of last season is sustained, he could actually post another mid-3.00 ERA again, but this time fully supported by his skills.

And now for the downside guys.

That is a huge difference for Yovani Gallardo. He has never posted SwStk% marks that would match his ERA, as his career best is a solid, yet unspectacular 9.2%. With only a league average ground ball rate and mediocre control, he is a surprise bust candidate. C.J. Wilson owners already have to worry about his huge innings jump of last year, but now the prospect of a decreased strikeout rate should have owners fearing the worst. I would not be surprised if Wilson is worthless in 12-team mixed leagues. Those of us, including me, who were optimistic about Jason Hammel’s breakout chances should be a little less so after seeing his name above. Add another mark against Ubaldo Jimenez for his chances of coming anywhere close to a repeat of 2010 or just breaking even for his fantasy owners who drafted him this season. Tommy Hanson continues to get hyped as one of the best pitchers in the game, but I struggle to see why. Admittedly, his stuff appears top-notch, but it simply has not generated results as strong as should be expected. His second half last year included a major K/9 decline to just a 6.4 mark and with just three strikeouts in his first nine innings to open the season, combined with a fastball velocity drop of 1.6 miles per hour, owners should be very concerned.

As a reminder, this analysis is not perfect. I am completely ignoring called strikes, which is a skill, and is a factor that influences strikeout rate of course. Some of the pitchers on the above lists may have called strike rates low or high enough that would indicate that his strikeout rate is not actually in for a fall or increase.