Bruce Rondon doesn’t use his fastball for strikeouts, but that’s OK

Bruce Rondon had somewhat of a breakout season in 2016. His ERA was a cool 2.97 and he struck out 11.15 batters per nine innings. Home runs were a problem at 1.24 per nine innings, but he kept his walk rate down to just 2.97 per nine. There are several positive takeaways from his season, such as a 3.70 FIP, a 2.95 SIERA, and a lower line drive rate (17.3 percent) than in years past. Even though they picked up the option on incumbent closer Francisco Rodriguez, a trade is still possible as the Tigers try to gain financial flexibility. And if they need to fill out the closer role for 2017, Rondon would not be as terrible choice as it was a few years ago when he did not have any major league experience.

However, there was one thing that bugged me about Rondon’s 2016 season. See, Rondon is known for his fastball velocity. Like a lot of flamethrowers, Rondon relies on a high strikeout rate (31.3 percent in 2016) to succeed. When Rondon got two strikes on a hitter, opponents only hit .108 against him with only one home run against. He has several times hit triple digits on the radar gun, topping out at 101 mph in 2016. Opponents hit his fastball at a .211 clip last year, which was a major improvement to the .356 average in 2015.

But the thing that sticks out is the strikeout distribution. Fourteen of his 45 strikeouts came on the fastball (31.1 percent) while the majority of his strikeouts (66.7%) came off his slider. How can Rondon, who has such an incredible fastball, have such a low strikeout rate on it? Will he be able to succeed like that in the future?

Well, it turns out many hard-throwers are in the same boat as Rondon. Here are some 2016 results on some of the fastest fastball pitchers.

Aroldis Chapman and Kelvin Herrera are the oddballs in this table for different reasons. All but Herrera are primarily two-pitch pitchers, with either a slider or curveball as their primary off-speed pitch. All but Chapman and Kimbrel get the majority of their strikeouts from their secondary pitches. All but Herrera were in the top 10 among MLB relievers in strikeout rate in 2016 (Herrera was at #22).

The two that Rondon might model himself after are Dellin Betances and Ken Giles. Rondon also had an average fastball velocity of 97.2 mph. His overall strikeout rate was at 31.3 percent, which is lower than Betances’ 42.1 percent and a little bit lower than Giles’ 35.7 percent. The percentage of strikeouts on his slider might be too high based on this data. Betances only had 21 of his 124 strikeouts (16.9 percent) come from his fastball while 19 of Giles’ 124 strikeouts were from his fastball (18.6 percent). It’s possible that Rondon is not getting enough strikeouts from his slider, as his fastball strikeout percentage is at 31.1 percent (14 out of 45).

Giles had an off year in 2016 with a 4.11 ERA, but he was fantastic in his first two seasons with an ERA under 2.00. His FIP was still good at 2.86, so a bounce-back 2017 seems like a good bet. Like Rondon, Giles’ home run rate ballooned in 2016 (1.10 homers per nine innings). Yet, he still utilized his slider as his main strikeout pitch. In 2015, 27 of his 84 strikeouts were from his fastball (32.1 percent) and in 2014, only 19 of his 64 strikeouts (29.7 percent) were from his fastball.

Betances was also sustainable in using his breaking pitch as his put away pitch. In 2015, only 38 of his 130 strikeouts came from his fastball (29.2 percent) and in 2014, 25 of his 135 strikeouts (18.5 percent) came on fastballs.

As Rondon continues to grow and mature as a pitcher, he’ll learn what works for him and what does not. What seems clear is that his slider is what works for him and he should embrace it even more in two-strike counts and save his fastball as more of a set-up pitch. Just like with Betances and Giles, Rondon can have great success by doing that as long as he makes the proper adjustments.