“Breakout” can mean different things to different people. It can mean a prospect or untested young big leaguer establishing himself as a valuable regular. It can mean a relative unknown becoming an impact player. It can mean a well-known star making the leap to full-blown superstar, perhaps even following up a “breakout” one year with an even bigger “breakout” the next. Your own definition may vary, but in PECOTA’s case “breakout” is all about out-performing track records.

PECOTA assigns each player a “breakout rate” for the upcoming season based on their odds of beating their established level of recent performance by at least 20 percent, with historical player comps serving as an important factor. Because the entire system is based on regressed-to-the-mean, 50th percentile projections, breakout rate identifies the players most likely to leave that in the dust for their 70th, 80th, and 90th percentile upsides.

Stars like Madison Bumgarner and Noah Syndergaard have relatively high breakout rates for 2017, but it’s not because PECOTA projects them to significantly improve upon their already great 2016 seasons (for Bumgarner, that would presumably mean becoming a full-time position player during the four days between each start or something). Instead, the system pegs them as the players most capable of rising above their 50th percentile projections.

Earlier this week I covered PECOTA's favorite position player breakout candidates and below you’ll find 10 starting pitchers assigned a high breakout rate by the system. I think it makes sense to focus on untapped upside, so I’ve removed established stars like Bumgarner, Syndergaard, and Gerrit Cole from the mix and also limited the pool to pitchers projected to throw at least 100 innings.

Aaron Nola, Philadelphia Phillies

Top Three Same-Age Comps: Gerrit Cole, Carlos Martinez, Phil Hughes

Nola posted a 4.78 ERA and missed the final two months with an elbow injury, so he’d probably like to forget 2016, but buried within those uglier aspects of his first full season were a bunch of promising secondary numbers. Among the 137 pitchers to throw at least 100 innings as starters last season he ranked seventh in ground-ball rate and 20th in both strikeout rate and K/BB ratio. Better yet he was fifth in DRA with a sparkling 2.72 mark that put him three spots ahead of Cole Hamels (2.84). If rest, rehab, and platelet-rich plasma injections don’t do the trick for him all bets are off, but PECOTA thinks Nola has shown a lot more upside already than his ERA suggests.

Carlos Rodon, Chicago White Sox

Top Three Same-Age Comps: Madison Bumgarner, Scott Kazmir, Mike Leake

Rodon threw more strikes last year despite Chicago's awful pitch framing, slicing his walk rate by 31 percent, but that mostly just led to batters teeing off on his fastball. Opponents slugged .570 against his heater and too often it was a struggle to complete six innings. His slider, on the other hand, is one of MLB’s most dominant breaking balls, holding opponents to a .155 batting average through 304 career innings. Without improved fastball command Rodon may be destined for the Francisco Liriano path of occasional flashes of brilliance within overall mediocrity, but he’s still just 24 years old and PECOTA has not given up on 200-strikeout, top-of-the-rotation upside if Don Cooper can work some magic.

Jameson Taillon, Pittsburgh Pirates

Top Three Same-Age Comps: Alex Cobb, Robbie Erlin, Carlos Carrasco

After missing all of 2014 and 2015 following Tommy John surgery Taillon returned stronger than ever at age 24, making 10 dominant starts at Triple-A and then shining in his 18-start debut with the Pirates. Taillon’s control was decent before going under the knife, but his comeback season featured a grand total of 23 walks in 166 innings to go with a mid-90s fastball and a pair of good off-speed pitches. It’s a rare combination of stuff and accuracy, which is why PECOTA views him as a ready-made impact starter and gives Taillon a chance to reach top-of-the-rotation status in his first full season. Health will always be a factor for Taillon, but the talent is undeniable.

Jon Gray, Colorado Rockies

Top Three Same-Age Comps: Gio Gonzalez, Edinson Volquez, Michael Pineda

Gray’s raw numbers may never jump off the page thanks to calling Coors Field home, but the third pick in the 2013 draft showed ace upside in his first full year. His fastball was fifth-hardest among qualified starters, but Gray’s high-80s slider was the real weapon and held opponents to a .180 average. Gray had the best strikeout rate and second-best K/BB ratio in Rockies history among pitchers with 150-plus innings and racked up double-digit strikeouts six times, including a 16-strikeout, zero-walk shutout (of the Padres, but still) in September. To have a 50th percentile ERA projection under 4.00 for Colorado is an accomplishment, but PECOTA thinks he’s capable of going below 3.50.

Lance McCullers, Houston Astros

Top Three Same-Age Comps: Alex Wood, Mat Latos, Jair Jurrjens

Shoulder and elbow injuries limited McCullers to 14 starts last year, but his potential to dominate was on full display as he missed enough bats to post a 3.22 ERA despite a preposterously high .383 BABIP. He’s far from a fully formed ace at 23—in addition to durability concerns, his control and fastball command need plenty of work—but McCullers has racked up 235 strikeouts in 207 career innings thanks to an absolutely filthy curveball. PECOTA loves his upside, but to reach it he’ll have to stay healthy and improve his fastball consistency to get ahead in enough counts for the curveball to unleash its full potential.

Matt Andriese, Tampa Bay Rays

Top Three Same-Age Comps: Jimmy Nelson, Joe Saunders, Adam Warren

PECOTA is a big Andriese fan, projecting him as a two-WARP pitcher at the 50th percentile and viewing him as having significant breakout potential at age 27. Andriese has repeatedly gone up and down from the minors to the majors and back and forth from the rotation to the bullpen. He’s generally fared very well as a reliever and been mediocre as a starter, struggling to get through a lineup multiple times. When his performance in the different roles gets mixed together the end result is a rosey projection, but there’s reason to be skeptical of Andriese’s upside as a full-time starter. Or maybe PECOTA is just onto something with an overlooked player.

Mike Montgomery, Chicago Cubs

Top Three Same-Age Comps: Joe Saunders, Alex Colome, David Phelps

Montgomery went from top prospect to afterthought to intriguing midseason pickup to recording the last out of the World Series, and now he might finally have his breakout at age 27. He’s had success starting and relieving, and Joe Maddon certainly liked having Montgomery available in the bullpen to put out fires in all sorts of different situations, but the Cubs seem committed to giving him an opportunity to claim a rotation spot. Montgomery has regained some fastball velocity as the injuries disappear further into the rearview mirror, but it’s his plus cutter and plus changeup that give him a chance to be an impact starter.

Sean Manaea, Oakland Athletics

Top Three Same-Age Comps: Danny Duffy, Felix Doubront, Patrick Corbin

Manaea is huge and throws reasonably hard, but deception and off-speed stuff are the keys to his game. Well, that and staying healthy. As a top prospect in the Royals’ system Manaea was repeatedly derailed by injuries and even last year, while putting together a nice rookie campaign for the A’s, he missed time with minor ailments. He also had a 3.52 DRA in 145 innings, shutting down lefties and posting a nice 96/33 K/BB ratio against righties (albeit with too many homers). PECOTA is a believer, projecting him for a sub-4.00 ERA at the 50th percentile and a 3.54 ERA at the 70th. If he stays off the disabled list, the slider and changeup can do plenty of damage.

Tyler Skaggs, Los Angeles Angels

Top Three Same-Age Comps: Martin Perez, Marcus Stroman, Dallas Braden

Skaggs went nearly two full years between major-league appearances thanks to Tommy John surgery in late 2014, but he was anything but rusty in 10 second-half starts for the Angels. His velocity was up a tick from his pre-surgery days and Skaggs struck out 50 batters in 50 innings. His mechanics, control, and overall health loom as possible stumbling blocks, but PECOTA sees Skaggs as a solid mid-rotation starter in 2017 and thinks there’s plenty of additional upside. His comps list is littered with dinged up former top prospects: Martin Perez, Marcus Stroman, Jaime Garcia, Justin Masterson, Drew Pomeranz, Matt Moore, Patrick Corbin.

Zach Davies, Milwaukee Brewers

Top Three Same-Age Comps: Gio Gonzalez, Vance Worley, Matt Harvey

BP’s new command/control data shows Davies as Kyle Hendricks 2.0, getting the most out of underwhelming raw stuff by leading MLB in Called Strikes Above Average last year (Hendricks ranked third while winning the ERA title). His fastball often fails to crack 90 mph, but he works the edges of the strike zone brilliantly by avoiding damage and coaxing borderline calls in his favor. In decades past we might look at a soft-tosser like Davies with a modest strikeout rate and assume that his success would be short-lived, but our increased ability to quantify his skill set shows him in a much more favorable long-term light.

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Rodon was crucified last year by the "framing" of White Sox catchers. He couldn't buy a low strike, and that's where he likes to work. Even substandard framing would be a massive improvement. I look for big things from Rodon this year.
"Because the entire system is based on regressed-to-the-mean, 50th percentile projections, breakout rate identifies the players most likely to leave that in the dust for their 70th, 80th, and 90th percentile upsides."

This makes no sense. by definition, every player has a 10 percent chance of exceeding the 90th percentile of his projection, a 20 percent chance of exceeding the 80th percentile, etc.
I hope a BP staffer provides a definitive answer.

My take is that Pecota is somewhat aware of its "error bars". The improvement number suggests the distance to the upside error bar, the collapse suggests the distance to the downside error bar.

That's simply based on my attempt to make sense of the information provided. I have no inside knowledge.
Its a bit misstated, Improve / Breakout / Collapse / Attrition are based on the chances relative to the player's established performance level over the previous 3 seasons.

For example, look at Clayton Kershaw. His 3 year established performance level is very high, and his weighted mean projection is lower, but he has a 43% improve rate (eg, PECOTA thinks that 43% of the time, his season will be better than his past 3 average). However, his worst options are significant declines, so his weighted mean is substantially lower because those extreme downsides drag his mean projection down. He is a pitcher, so there are always the chances of extreme decline and few innings pitched due to injuries. All of those except attrition look at performance rate, so Kershaw doesn't take a hit for his lower WARP last year since he was still fantastic when he did pitch.

You can find the exact improve/collapse/breakout/attrition rates in the PECOTA spreadsheet if you have access to that. You can find it under Home > My Account > Digital Downloads.

Player performance curves aren't linear, so the difference between the 10th percentile and 30th percentile, or the 60th and the 90th, are likely to be much more than 20 or 30% in terms of production.

PECOTA's a complex beast and when you are dealing with segments that are confusing or hard to understand, I strongly recommend the PECOTA segment of the glossary as those entries have existed since it was created by Nate Silver and Nate is very, very good at being specific.
When you look at a PECOTA WARP projection, you have to remember that there are many ways to arrive at that. To continue to use the Kershaw example, PECOTA projects 5.1 WARP, similar to last year.

He could get there by pitching another 145 innings at the level he did last year.

he could get there by pitching 210 innings as merely an excellent pitcher instead of a generational talent level.

he could get there by only pitching 100 innings as the next coming of Pedro Martinez before getting injured.

The odds of him putting up another 7.5 WARP season aren't great by PECOTA's estimation because any of those things can happen and prevent him from combining generational talent + 210 innings to get back to the 7-8 win level.
Mr. Gleeman, what you say.? You have been challenged to provide sine depth to your words?