age-31: An Unlikely Hero

Brewers fans and analysts cannot get enough of Junior Guerra, and rightfully so. In the midst of a rebuilding season, Guerra presents a rather large set of intriguing traits:

  • Guerra made his first MLB start in his age-31 season.
  • The righty was one of the “quietest” no-risk moves made by GM David Stearns during the offseason, and represents “pure reward” for the Brewers.
  • Guerra profiles as a potentially high-strikeout master on the mound.
  • Even better, rather than following a traditional secondary pitch sequence (relying primarily on a slider or curveball), Guerra joins a group of pitchers that chooses from the change / fork / split / screwball spectrum for their major neutralizing pitch.
  • As BPMilwaukee’s own Jack Moore documented, splitter is something else. In a rebuilding season, it represents an excellent aspect of the game to cheer on (much like Ben Sheets’s 2004 curveball).
  • Better yet, the rookie is having quite a good start to his season, which is a breath of fresh air within a struggling rotation.

Most analysis of Guerra justifiably focuses on the righty’s splitter. The pitch features a steep, dramatic drop that gives him a chance to wipeout batters. BPMilwaukee’s own Ryan Romano also detailed how Guerra uses pitch sequencing to improve the impact of his main off-speed offering. Yet, fans should arguably be focused even moreso on Guerra’s age, as the righty is (thus far) poised to accomplish a one-of-a-kind season in MLB’s divisional era: Guerra has the opportunity to start the largest slate of games ever pitched by a hurler debuting as a starter during their age-31 season.

Years # of age 31 P (avg. per year) GS debut at 31 % GS debut
1969-1979 159 (14.5) 1 0.6%
1980-1989 216 (21.6) 4 1.9%
1990-1999 282 (28.2) 3 1.1%
2000-2009 344 (34.4) 4 1.2%
2010-2016 235 (33.6) 2 0.9%

Since divisional play began in 1969, 1236 pitchers have worked during their age-31 season. It has been quite rare to debut as a starter at age-31, however. The first divisional era age-31 starting pitching debut was made by Oscar Zamora for the 1976 Cubs; Zamora started 2 of 40 games that year, having worked as a reliever in 1974 and 1975 for the Lakeview Nine. Prior to reaching the MLB in 1974, Baseball-Reference shows that Zamora spent a decade working through the minors, mostly in the Eastern League and American Association. The Cubs purchased Zamora out of the Astros’ system, and the righty even served as a relatively early free agent in the MLB (1977).

Zamora’s experience is rather standard among age-31 starting pitching debuts: he didn’t start another MLB game after his age-31 season. For example, the Brewers had their own age-31 starting pitching debut in 1987 with Mark Clear, a quality reliever acquired prior to 1986 via trade (and re-signed prior to 1987). According to The Neyer / James Guide to Pitchers, Clear was a curveball-first pitcher who also developed a slider in Milwaukee. In his June 30 start in 1987, Clear posted his roughest outing of the year, facing the stacked Tigers offense at County Stadium in what would become his only MLB start.

Fourteen total pitchers have made their first MLB start during their age-31 season during the divisional era (including Guerra), and nine of 13 failed to make another MLB start after age-31. Guerra’s feat is exceptionally rare, and the track record of age-31 starting pitching debuts leads one to wonder how to project Guerra’s future potential.

Age 31 GS debut Previous MLB G MLB G after age 31 (GS) age 31 K / BB / HR (IP) age 31 DRA
Oscar Zamora (1976) 108 10 (0) 27 / 17 / 8 (55.0) 3.95
Doug Corbett (1984) 181 87 (0) 48 / 30 / 2 (85.0) 3.61
Mark Clear (1987) 394 29 (0) 81 / 55 / 9 (78.3) 4.22
Ubaldo Heredia (1987) - 0 (0) 6 / 3 / 2 (10.0) 4.82
Stew Cliburn (1988) 45 0 (0) 42 / 32 / 11 (84.0) 4.91
Dwayne Henry (1993) 212 10 (0) 37 / 39 / 6 (58.7) 5.50
Darren Holmes (1997) 316 199 (0) 70 / 36 / 12 (89.3) 4.80
Al Levine (1999) 71 295 (6) 37 / 29 / 13 (85.0) 5.59
Jose Contreras (2003) - 281 (166) 72 / 30 / 4 (71.0) 4.79
Marty McLeary (2006) 3 4 (0) 8 / 6 / 1 (17.7) 5.58
Dan Giese (2008) 8 7 (1) 29 / 14 / 3 (43.3) 3.14
Justin Lehr (2009) 66 0 (0) 33 / 28 / 14 (!!) (65.3) 6.79
Hisashi Iwakuma (2012) - 91 (91) 101 / 43 / 17 (125.3) 4.04
Junior Guerra (2016) 3 ??? 36 / 12 / 2 (36.3) 3.11

Recent age-31 debuts in the form of International Free Agents provide more tantalizing comparisons for Guerra. Jose Contreras signed out of Cuba as an amateur free agent in 2003, claiming nearly 100 games pitched in the Cuban National Series. Almost a decade later, Hisashi Iwakuma signed as a free agent with the Mariners, having pitched for 11 years in the Japanese Pacific League. Alongside swingmen/set-up men/journeymen Darren Holmes and Al Levine, Contreras and Iwakuma have the most post-31 experience in the MLB from this group. These international players also have the best track record, as Contreras posted five better-than-average cFIP (50.0 IP+) seasons in his career, while Iwakuma has served within a bona fide 1-2 punch in Seattle.

In some sense, Iwakuma’s ascent and Contreras’s fluctuations offer two realistic poles for discussing Guerra’s potential. First, like Contreras, one must note that the Brewers righty can be a serviceable pitcher and work through some hiccups in his career; it doesn’t have to be a fairy tale for Guerra to help Milwaukee. Second, like Iwakuma, one must consider the benefits of a strong off-speed pitch and good peripheral performance for Guerra. Thus far, Guerra’s biggest question mark remains his groundball:flyball ratio, although the righty arguably limits the damage with his strong strike out and walk rates.

Perhaps most interestingly, Guerra’s arsenal almost perfectly mimics that of Contreras and Iwakuma in general orientation toward the forkball / splitter spectrum. To be fair, there is no confusing Contreras’s knuckling, tumbling soft fork with Guerra’s hard-slicing variation. The general point is that it is a fascinating accident of history that two of the most successful arms from the age-31 starting debut group share the same basic pitching profile for their most popular offspeed pitch (neutralizing “split / fork” spectrum, instead of breaking “curve / slider” spectrum).

“Full Time” Comps K% / BB% / HR% GB% / FB% / LD% Pitch Sequencing (source)
2003 Contreras 24.6 / 10.2 / 1.4 49.5 / 28.6 / 22.0 mid-90s Fastball / Forkball / Slider / Change (Neyer James)
2012 Iwakuma 19.5 / 8.3 / 3.3 52.2 / 27.3 / 20.5 Four-Seam (90.9)/ Sinker / Split / Slider / Curve (Brooks)
2016 Guerra 24.7 / 8.2 / 1.4 38.9 / 40.0 / 21.1 Four-Seam (94.7) / Split / Slider

[Incidentally, while digging through seasonal data, another interesting splitter profile emerged in an age 31 season: Ryan Dempster made an astonishing role change from closer to starter in 2008, during his age 31 season, and he also became a serviceable (or better) starter thanks to a fastball / splitter / slider general profile. Mike Marshall also produced his unbelievable 208.3 IP relief season as a screwball wielding 31-year old, adding to a pre-splitter version of this “neutralizing” profile. Mike Scott is another obvious age-31 breakout comparison with the split, and Scott produced several solid seasons after his elite breakout.]

Although pitch f/x data was not available for Contreras’s debut, the righty thankfully snuck within the publication timeframe for the Guide to Pitchers by Rob Neyer and Bill James. Later Brooks Baseball entries confirm that Contreras’s forkball was his slowest pitch, and in some successful years (like his 2008 87 cFIP season) the righty equally selected his sinker, slider, and fork. While some of Contreras’s command woes are instructive for Guerra’s path, so too is that veteran’s shift to equal pitch selection (or pitch sequencing development). One might expect Guerra to adjust toward his fastball and slider to keep hitters guessing as the season moves on and scouting reports circulate. This adjustment could be necessary to improve that groundball rate.

In the worst case scenario, Brewers fans are treated to a truly historical campaign in 2016, and that’s the highlight for Guerra. Contreras worked nine MLB starts in his debut season, while Iwakuma reached 16; if Guerra keeps his rotational spot and remains healthy, he stands a good chance of starting the most games of any age-31 starting pitching debut during the divisional era. This is a thrilling feat that scores one for the “age ain’t nothing but a number” camp.

In the best case scenario, the righty remains in the rotation, and continues to serve as a serviceable-to-surprising option. Obviously reality offers several notches between those poles, from a value-seeking trade to potential relief roles (unleashing Guerra’s split in short stints could catapult the righty to poor man’s Eric Gagne status, for those that remember the diving “vulcan change”). At any rate, don’t get sick of the hype and coverage, embrace it: this journeyman could produce a rare career arc, and it starts here.


BaseballProspectus. BaseballProspectus, LLC. [for advanced stats & Brooks Baseball.]
Baseball-Reference. Sports-Reference, LLC. [for historical data]
Rob Neyer and Bill James. The Neyer / James Guide to Pitchers. New York: Fireside, 2004.

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