Hitter Breakouts: Stickiness Of Stats

A few days back, I start the process of trying to find breakout hitters. I found some possible traits which point to hitters breaking out but didn’t get into the stickiness of the stats over different time frames. I’m back to see how the “breakout” stats main their values over time.

For a quick review, here are the claims I made in the previous article.

Overall, here are the rules.
• K%-BB% (plate discipline) changes by +/- 4.5%.
• Flyball rate (FB%) changes by +/- 3%.
If the above two items can’t explain the change move onto the following three points.
• Pull% change (only) by +/- 5% this value can good or bad depending on the hitter’s other traits.
• Raw power can start decline once a player reaches 30-years-old.
• BABIP changed by +/- 30 points. (A change in plate discipline can cause this change)

I will just start walking through the points comparing the results for the year after the breakout. Also, I will look for hitters breaking out in the season’s first month and how those stats carried forward.

Plate Discipline (K% – BB%)

Year-to-Year: The gains held decently with the average hitter seeing their plate discipline gains drop by only a third. The more the improvement, the more it stuck. I’m sure these gains are baked into most projections but see if other owners agree by checking on the breakouts average draft position.

Justin Turner, Justin Smoak, and Steven Souza Jr. have each seen their K%-BB% drop by over 10% points. They will be nice test cases for next season.

March/April to full season: The gains are generally kept but only to the tune of 33%. To achieve, on average, an end-of-season 4.5% improvement, a hitter needs to have an 11% or better early-season change.

Looking at just hitters from this season, the breakouts include Aaron Hicks, James McCann (good for a catcher), Steven Souza Jr., and Robbie Grossman.

Flyball Rate (FB%)

Year-to-Year: The year-to-year FB% results almost line up perfectly with plate discipline values with hitters only losing a third of their gains a year after the improvement. Most projection systems don’t take batted ball data into account, so owners may want to target these hitters on draft day.

March/April to full season: The early season gains stick with hitters maintaining around 40% of their first-month gains. Those with an 8% gain are expected to maintain at least a 3% gain.

Now, a word of caution, be careful buying hitters with a 20% or more improvement. They see a production decline because of too many flyballs.

Pull Rate (Pull%)

Year-to-Year: Only 55% of the Pull% gains are maintained from year to year.

March/April to full season: While year-to-year pull rates aren’t kept, early season pull rates are, with 42% of early season gains maintained.

Note: This will be its own future article as there is no good right answer, pull or spray, for each hitter. More context is needed and I am trying to keep the process simple.

I’m getting to the point where I just may remove the pull rate from this process.

Late Career Power Drop (.100 ISO drop)

Year-to-Year: This decline was fairly sticky with over 70% of the drop maintained. Also, only eight of the 88 hitters saw their ISO rebound. The average age for these hitters was 31-years old with the standard deviation of 4 years. Keeping the age cutoff at 30-years-old seems fine but it should not be a hard and fast number. Hitters age differently.

March/April to full season: Owners should expect half of an early season ISO drop to stick. These hitters don’t get their previous season’s power back. Also, the age still matches up with 30.5 being the decliners’ average age.

One aspect I tested was if older players didn’t bounce back as much as the season went on. I couldn’t find any truth to this statement. Age didn’t seem to affect the amount of rebound.


I think I am on the right track by concentrating on flyball rate and plate discipline. The factors correlate decently from season-to-season and in- season. They’re not perfect, but they can help to remove a lot of the noise surrounding hitters and narrows down the search for those few hitting stats to focus on.

Jeff, one of the authors of the fantasy baseball guide,The Process, writes for RotoGraphs, The Hardball Times, Rotowire, Baseball America, and BaseballHQ. He has been nominated for two SABR Analytics Research Award for Contemporary Analysis and won it in 2013 in tandem with Bill Petti. He has won four FSWA Awards including on for his Mining the News series. He's won Tout Wars three times, LABR twice, and got his first NFBC Main Event win in 2021. Follow him on Twitter @jeffwzimmerman.

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6 years ago

Great articles. I’ve been watching Rosario and Buxton of the Twins try to exert more plate discipline the last year and a half. Rosario started identifying better pitches the 2nd half of 2016. His WRC+ shot up but he still had poor plate discipline (K%-BB% = 22.3% in 2016). His plate discipline was much better to start 2017 but he didn’t hit much in April. Since then, he’s retained his discipline and improved every month (K%-BB% = 10.4%, 158 WRC+, 2nd half). I think most of the discipline will stick.

Buxton had a nice September 2016, showing a lot of power. He came back with a truly horrible Mar/Apr (K%-BB% = 25.7%, 22 WRC+). He’s made adjustments and is hitting better in the 2nd half (14.5%, 120). Still, his in-game power hasn’t reached anywhere near his potential. I hope Buxton follows Rosario and begins to add power in the next year. He should definitely be a test case.