Late in the 2017 season, I approached Sergio Romo to ask about backup sliders. More specifically, I wanted to know if he’s ever thrown one intentionally. A handful of pitchers to whom I’ve spoken have experimented with doing so. It can be an effective pitch when well located; hitters recognize and react to a slider, only to have it break differently than a slider. As a result, they either jam themselves or are frozen.
Romo, of course, has one of the best sliders in the game. The 34-year-old right-hander has lived and died with the pitch for 10 big-league seasons, throwing his signature offering 52.4% of the time. Among relievers with at least 250 innings, only Carlos Marmol (55.5%) and Luke Gregerson (52.7%) have thrown a slider more frequently over that span.
What I anticipated being a short conversation on a narrow subject turned into wider-ranging, and often entertaining, meditation on his slider (with a look at Zach Britton’s sinker thrown in for good measure). It turns out that Romo’s backups are all accidental — the exact mechanics behind them remain a mystery to him — but he does know how to manipulate the ones that break. He’s also knowledgeable about his spin rate, thanks to his “player-profile thingy.”
Romo, who has pitched for the Giants, Dodgers, and (more recently) the Rays, sat down to talk sliders when Tampa Bay visited Fenway Park last September.
Sergio Romo: “I like to throw my breaking ball on both sides of the plate, and there have been a couple of times where people have told me, ‘Hey, thats a nice backup slider.’ I’ve been like, ‘Well, I meant to throw it on that side of the plate, but I don’t know what they saw in terms of ‘it backed up.’ Maybe it looked that way, but I was just trying to get it front hip. It was an accident as much as anything.
“I don’t precisely know what action, what motion, you do that makes it back up. Like, do you get underneath it more? Do you get behind it more? Do you get around it more? Push it more? Choke it? I mean, there are times I maybe pulled off, or maybe I was out in front. Maybe I didn’t land before I threw the ball. There are certain things where I’m like, ‘Meh,’ but I haven’t been able to fully figure out what’s made it back up when it has. If I knew, then yeah, I could kind of practice it. I could be like, ‘Hey, you know what: if I did this, maybe it would do that again? Ofr, ‘If I did this, maybe it would it do that.’
“Playing catch is how I figured out how to differentiate between my sliders — the things I do to throw the back-door slider, the front-hip slider, the back-foot slider, the swooper, the short hard one. There were things I was able to figure out in those areas, but in terms of what I did to get it to back up… again, I still don’t know.
“I’ve dropped my elbow to try to see what that does. I’ve gotten under a couple on purpose to see if maybe it will go slower or more down or whatever. I’ve seen more of those back up, but I don’t exactly know if that’s why.
“I’ve had plenty of ruts in my career, but a lot of the times I’ve felt like I didn’t have my slider it was more about confidence. I wasn’t throwing it with the same conviction. I was kind of passive about it — maybe ‘tentative’ is a better word — as opposed to aggressive.
“I think the rotation that I create on the ball, the spin… I get more revolutions. I think I’m averaging around 2,800 [RPM], so I’m something like 400 above average*. I’ve seen that in my player-profile thingy.
*The average spin rate on Romo’s slider this past season was actually 2,894. The MLB average was 2,362.
“The way Zach Britton throws his two-seamer, his sinker — at least from what I’ve been told — is different. He kind of rolls it. And I don’t know how he creates that velocity. His sinker isn’t one of your typical ones. It’s ‘Boom!’ I mean, it’s really weird, because it doesn’t just go [Romo makes a whooshing sound with a gradual downward motion]; it literally goes [Romo makes whooshing sound of increasing volume, sharp at the end, with a more pronounced downward motion]. I mean, it’s unique. It’s gnarly.
“The way I throw my slider is different, too. The rotation I get on the ball, the spin, is almost like a bowling ball thing. My slider will come out and it will be spinning, spinning, spinning, and then as soon as it catches, it picks up speed and shoots the other way. Whoosh! It’s like when you bowl. You throw the ball, and then as soon as it catches, it shoots with more speed and power. Right? That’s kind of what my slider does.
“I’ve been told that it looks like it almost stops for a couple of inches. It’s almost like it gets there, and then goes [Romo make a whooshing sounds, pauses, makes another whooshing sound]. It’s just different. I throw it hard. I throw it aggressive. I reach back for it when I throw it.
“I know I have to change speeds on my slider, though. I know I have to take some off and put some more on. That’s my… I mean, it’s like other guys throwing sinkers, cutters, four-seamers… they take something off to add movement. The four-seamer is right at you. These guys are throwing 95-100, and then they’ll come at you with a sinker that’s 92-94 and then a cutter that’s 90-92. You’re sitting there going, ‘dang.’ Me, I have three sliders. I have a slow big one, a short hard one, and one that goes down. I have to use all of them, because hitters are good.
“You want to get beat on your best pitch, but you can still probably throw too many sliders. Like, a difference for me this season — changing uniforms, so to speak — the difference between the two places is my fastball usage. I’ve used my fastball a lot more lately. But it’s all relative. My 95 comes in another way. My 95 is a breaking ball. A lot of guys sit gas, but I’m backwards. I just need to pick and choose when to use my fastball. Sometimes when I throw one, the hitter doesn’t know what to do. Right?”
David Laurila grew up in Michigan's Upper Peninsula and now writes about baseball from his home in Cambridge, Mass. He authored the Prospectus Q&A series at Baseball Prospectus from December 2006-May 2011 before being claimed off waivers by FanGraphs. He can be followed on Twitter @DavidLaurilaQA.