So, Yu Darvish is off to a pretty good start to 2013. Through eight starts this season, the Ranger’s right-hander currently sports the following statistics:

GS K% BB% HR/FB ERA- FIP- SwgStr% 8 39.0% 8.8% 13.9% 62 56 15.7%

Darvish currently ranks first (or tied for first) among qualified starters in K% and SwgStr%, and he has posted the 6th best adjusted FIP in the league (56 FIP-). After a blazing start, his ERA- has dropped to 20th and his HR/FB now ranks 84th, but overall it’s clear Darvish has been a beast in 2013.

After watching this wonderful footage from Darvish’s dismantling of the Angels last night I was struck by how slow is curveball actually is.

Our own Carson Cistulli isolated his four slow curves from that night — check out the final bender to Mike Trout, resulting in a strikeout in the 6th inning. And, yes, that was 61 mph.

I wondered whether the differential between Darvish’s fastball and curveball was the largest in the league. And, so, to the data I went.

I pulled the average velocity by pitch type from our PITCHf/x leaderboards and calculated the difference between each pitcher’s hardest thrown pitch and their slowest. I eliminated any pitches coded as an eephus pitch to get a more realistic read.

Through May 13, Darvish in fact has the greatest differential between his fastest and slowest thrown pitches at 26.1 mph. That’s 5 mph greater than the next starter, Chad Billingsley (21.1 mph) (note: Max and Min refer to the average velocities for a pitchers fastest and slowest pitches):

Taking a look at the past four years, Darvish’s differential in 2013 ranks first among all starters since 2010. Darvish’s 2012 ranks 5th on the list:

Just eye-balling these lists it would appear that larger differentials in velocity are associated with better performance (i.e. ERA-, FIP-, K%). In fact, a pitchers velocity differential is significantly correlated with their K% (.167), HR/FB (.167), ERA- (.158), FIP- (.144), and IFFB% (.131). If we break starters up into various percentiles — based on the differential between their fastest and slowest pitches — we can better see the difference in their performance (weighted by innings pitched):

Metric 90th P-tile 75th P-tile 25th P-tile ERA- 90 92 100 FIP- 92 93 100 HR/FB 9.0% 9.3% 10.4% IFFB% 10.4% 9.9% 8.7% SwStr% 8.7% 8.6% 8.4% K% 20.2% 19.5% 17.7%

On average, starters with differentials at or above the 75th percentile (15.3 mph) produce adjusted ERAs and FIPs about 7-8 points lower than those at or below the 25th percentile (10.7). Greater differential pitchers also strike out about two percent more of the batters they face (19.5% vs. 17.7 K%).

Between the correlations and the percentile comparisons it’s clear that, while making a difference, overall change of pace isn’t a huge differentiator for pitchers. However, it does have some impact and right now no one is doing it better than Yu Darvish.