What’s Behind Tony Santillan’s Emergence as a Reliever?

What’s Behind Tony Santillan’s Emergence as a Reliever?

A few things have gone right for the 2021 Reds. Jonathan India and Tyler Stephenson have emerged as impressive and dynamic rookies who look destined to be franchise cornerstones. Joey Votto is putting together a season for the ages and aged. Jesse Winker, while healthy, was one of the best hitters in baseball. Sonny Gray, Luis Castillo and Tyler Mahle formed an excellent top-three for the rotation.

You can always find success stories in the bullpen. But given the nature of most relievers who have been around the block, the good moments are fleeting. But in 2021 the Reds may have found a relief arm that could provide lasting value.

As we turn the scorecard to 2022, let’s look at 24-year-old Tony Santillan, a player who could be an important part of next year’s team.

Journey through the Minors

The Reds acquired Tony Santillan in the second round of the 2015 draft. The 18-year-old had just played for Seguin High School in Arlington, Texas. Matt Wilkes wrote a detailed getting-to-know post about Santillan in May when the young right-hander was called up for his major league debut in the aftermath of a Sonny Gray trip to the IL.

The short version: After a short adjustment period, Santillan emerged in A and AA ball as a better than average prospect, being named as a top-100 guy by Baseball America in 2018. Santillan stumbled, in 2019 which he attributed in part to pitching through a knee injury.  He spent the 2020 COVID season at the Reds alternate site. While he was never called up to the big league club, Santillan was one of several Reds — like Jonathan India — who seemed to benefit from the development program there.

If you want more detail about Santillan’s journey through the Reds minor league system, read Matt’s post.

2021 Ping-Pong

Tony Santillan began the 2021 season in AAA and made six starts from May 5 to June 4. In those 32.1 innings he struck out 45 and walked 12 batters, so he was continuing the progress he made in 2020. In 99 of  his 101 minor league appearances, including those six games for the Bats, Santillan had been a starting pitcher.

And it was as a part of the Reds rotation the 24-year-old debuted at the major league level on June 13.

Santillan made four starts in a Reds uniform. He got through five innings once. Santillan was hit hard. For example, the Padres put 10 balls in play against him and five were hit at 99.7+ mph, four in excess of 105 mph. Santillan struggled to miss bats that game, registering just three whiffs on 21 swings. Against Atlanta, he allowed an average exit velocity of 92.1 mph on 13 batted balls. Santillan’s final start, a rematch with the Padres was another dud.

So, when Sonny Gray returned the club sent Santillan (not Vlad Gutierrez) back to AAA on June 30. But this time he was assigned to the bullpen.

Santillan made a single relief appearance in AAA before being recalled to the Reds with Sonny Gray headed back to the IL. Santillan then appeared six times from Reds bullpen before being sent back to AAA on July 30 when Michael Lorenzen was activated from the IL. Two-plus weeks later, Santillan rejoined the 2021 Reds, this time for good. All of his appearances after the first four were as a reliever.

Starter vs. Reliever Results

Tony Santillan has faced 82 batters as a starter and 89 as a reliever, so the sample sizes in each role, while still relatively modest are about the same. It’s easy to find the public-facing stats like batting average, slugging, ERA, etc. that show Santillan has been better as a reliever. But we need to dig deeper to figure out if the improvement was real or a mirage.

It’s possible that Santillan has been better as a reliever simply due to luck on where balls land, or how good his defenders were on a certain day, or how well they were positioned. That data shows up in a pitcher’s BABIP (batting average on balls in play). And, indeed, Tony Santillan has a large BABIP variance based on his role in the game. He has been about 100 batting average points luckier as a reliever than as a starter. That gap makes using stats like ERA and BA-against unreliable as a way to evaluate Santillan on the two roles.

In fact, the BABIP gap is so large it raises the question whether Santillan has actually been better as a reliever. Fortunately, we have ways to figure that out.

For one thing, we know that Santillan has been better in his bullpen role on balls that haven’t been hit into play. Check out his strikeout and walk numbers:

That first column may be the most important in this post. Santillan’s strikeout rate (which doesn’t depend on defense, luck, etc.) has been much higher as a reliever. His walk-rate, while still higher than league average, is down two percent out of the bullpen.

Several easy-to-access metrics normalize BABIP variance and focus on the outcomes over which the pitcher has most control. They are called “fielding-independent” and there are several, each slightly different. FIP normalizes for BABIP but gives the pitcher full credit for his home run rate. xFIP is FIP but also normalizes a pitcher’s home run rate based on how many fly balls he gives up. Finally, SIERA is an advanced version of xFIP that accounts for the type of balls hit into play. The fielding-independent data tells a consistent story:

Adjusting for the randomness that produced the 100-point BABIP variance, Santillan has been roughly two runs better per nine innings as a reliever.

We can also look at the quality of contact Santillan has surrendered in his two roles, factoring out the variability (defense, park, luck). Here is data on how hard batters hit off Santillan and the expected batting averages from that contact.

Santillan gave up a lot of hard contact as a starter. 51% of the balls hit off him were considered “hard-hit” compared to just 24% as a reliever. His average exit velocity was above average as a starter and been below average as a reliever. Translating that to batting average, if you look at the league-wide outcome for the balls hit with the quality that Santillan gave up, his xBA number as a starter was above average and his xBA as a reliever significantly below.

The fourth column of that chart (xwOBA) puts it all together. It includes strikeouts, walks, and quality of contact in terms of batting average and power. It weeds out all the noise that comes in stats like ERA and plain batting average. It shows that Tony Santillan has been much, much better as a reliever — quite excellent — than he was as a starter.

What’s Behind It

Given the small samples sizes (only four starts), drawing the conclusion Santillan has been better in the bullpen would be on more solid ground if we had metrics that involved larger numbers. It would be even better if we could pinpoint what was behind Santillan’s improvement as a reliever.

Higher Fastball Velocity The sample size here is over 300. It shows Santillan has gained a few ticks on his heater in the bullpen.

  • Starter FBv (94.3 mph)
  • Reliever FBv (95.7 mph)

If you’re wondering what difference that can make consider these league-wide numbers:

Santillan’s FBv difference is closer to 1.5 mph than 2 mph but you get the point. There’s a gigantic boost in success going from a 94-mph fastball to a 96-mph fastball. Santillan has been able to average just about 96 mph as a reliever. Most pitchers who move from a starting role to the bullpen experience this. Jeff Hoffman’s fastball has been about 1.5 mph faster as a reliever in 2021, too.

Here’s Santillan giving up a home run to Tommy Pham on a 94.2 mph fastball.


Here Santillan throws a 96.2 mph fastball past Kris Bryant.


And Santillan dialed up this fastball to 98 mph that Trea Turner watched for a called third strike.


Backing that up, Santillan’s fastball Pitch Value number has swung several runs from negative to positive as he moved to the bullpen.

Higher Slider Velocity Santillan has thrown more than 300 sliders for the Reds in 2021. It’s his clear #2 pitch and he’s used it a bit more as a reliever relative to his changeup. Just like with his fastball, Santillan has been able to throw his slider with more velocity.

  • Starter SLv (84.2 mph)
  • Reliever SLv (85.8 mph)

League-wide data for sliders shows — again, like the numbers for fastballs — that the difference in two mph, from 84 mph to 86 mph is significant in terms of strikeout rates, limited power and hard contact, and suppressing batting average. These factors were reflected in Santillan’s composite run allowance number for his slider:

  • Starter xwOBA on SL (.308)
  • Reliever xwOBA on SL (.203)

More First-Pitch Strikes Again, this is based on a larger sample size (171 batters). Pitching from the bullpen has allowed Santillan to throw more first-pitch strikes.

  • Starter First-Pitch Strikes (51.2%)
  • Reliever First-Pitch Strikes (55.1%)

The value of first-pitch strikes is easy demonstrate. Major league batters hit 60 percent worse once the count reaches 0-1 compared to if the count starts 1-0:

  • Count starts 0-1 .213/.260/.350 (wRC+ 67)
  • Count starts 1-0 .255/.378/.441 (wRC+ 127)
Tony Santillan’s Future

Tony Santillan as a starting pitcher was about 30% worse than the average major league pitcher. By moving to the bullpen, he’s been able to challenge hitters in the zone, throw his fastball and slider harder and emphasize his best two pitches more. As a reliever, he’s been 20% better than average. Most of the gain has been with his fastball, but pitches are interrelated. A better slider makes a fastball tougher to hit.

What this means for Santillan’s role going forward is unclear. You can make an easy case as a two-pitch pitcher he should stay in the bullpen. Santillan seemed to thrive coming out in relief. He’d be due for more high leverage spots next year. The data presented above is compelling.

On the other hand, Santillan does have a third pitch — a changeup that he throws mostly to left-handed batters. But he didn’t use it much (8%) even when he started. Moving Santillan back into a starter role depends on whether he could boost his fastball velocity over a 6-inning start. It’s possible his arsenal improvement over 2021 was due to experience and development, not shorter stints. If that’s the case, Santillan could be a valuable starter with a third pitch. Keep in mind he only had four starts, which is not much to go on.

While Tony Santillan’s future role with the Reds depends on Santillan himself, it is also affected by other pitchers in the organization. Will the Reds need more starters in 2022? Can they find able replacements in the free agent market or promote Hunter Greene and Nick Lodolo? How will Santillan compare there?

Tony Santillan still has room for improvement in that role, primarily getting his walk-rate down and working his changeup in vs. lefties. At minimum, the Reds have found a home-grown pitcher who looks like he’s going to be a successful reliever.

Photo: Jeff Speer (Icon Sportswire)

Steve Mancuso

Steve Mancuso is a lifelong Reds fan who grew up during the Big Red Machine era. He’s been writing about the Reds for more than ten years. Steve’s fondest memories about the Reds include attending a couple 1975 World Series games, being at Homer Bailey’s second no-hitter and going nuts for Jay Bruce at Clinchmas. Steve was also at all three games of the 2012 NLDS, but it’s too soon to talk about that.

2 Responses

  1. Crangis McBaseball says:

    Great information. Santillan looks like he is much more comfortable on the mound as a reliever. But that might be the result of gaining more confidence as the season has progressed. I’d like to see what the numbers are on Santillan’s inherited runners and inherited runners that scored. I looked around Fangraphs but didn’t see them there.
    There was a game, I think it was against STL at the end of July where Santillan came in with the bases loaded and no outs. He proceeded to retire the 3 batters he faced 1-2-3, two with K’s. It seemed like it was that game that really catapulted Santillan’s confidence level. His confidence level soared after that game and he has been a rather good component of the bullpen ever since.
    My hope for Santillan is he becomes that fireman to put out those late inning fires. The one we all hoped that Michael Lorenzen was going to be. Or even better, the closer for 2022. Santillan does have a closer’s demeanor and mentality. He kind of reminds me of a Lee Smith on the mound. The Reds could use that in the worst of ways.

    • beelicker says:

      Bell does this with all his relievers, using them in matched leverage situations. Need to check which part of the lineup which pitchers face. Mostly until very late in the season Santillan only faced bottom of the order hitters. He’d overwhelm the 7-8-9 spots, job well done, and then one of the higher leverage relievers would pick up next with the 1-2-3 the next inning. This is truly noticeable in Bell’s use management paradigm. Late in the season Santillan evolved into a top of the order leverage level reliever