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Rookie Redux
2004-09-23 12:30
by Mike Carminati

In an effort to drain every possible drop from the well, I have one final chapter in history of baseball rookies:

Effects on Winning:

First, I found that the percentage of rookies on a team correlated poorly to team success (.335 correlation coefficient). Then I took a look at teams' weighted ages and weighted experience level (i.e., weighted by percentage of games played) to see if they correlated to winning. They didn't either (0.3490 for team experience and 0.2157 for age).

Someone at Baseball Think Factory(which I still call Baseball Primer) suggested that perhaps it was a curvilinear relationship. That is, that teams with a large percentage of rookies and teams with a large percentage of vets would both perform poorly, while teams with a more balanced composition would perform best.

So I took my raw data and plotted Rookie Percent, Average Weighted Team Age, Average Weighted Team Experience, and Average Weight Team Debut Age (i.e., Age minus Experience). Unfortunately, they did not reveal a facile relationship to winning. I am unable to reproduce them here, but I'll hit the more salient points.

In all of the graphs (except debut age), teams that performed very poorly (with a winning percentage below around .375) had a large percentage of rookies and young, inexperienced players. As the winning percentage got lower the relationship got much stronger.

However, the rest of the graph ever so slightly did express this curvilinear relationship. But it was more like a dish than a bowl. Also, the percentage of rookies held between steady 15% and 20% for the rest of the graph. It was the most flat of all the graphs.

The Experience expressed the most arc, and the curve on the winning side of the graph (above .500) was slightly higher. With a winning percentage of around .400, the average experience level was between four and four and one-half years. It then increased to under six years at around a .475 winning percentage. The average seems to exceed six years slightly at a .550 to .575. Then it slopes down to about five and one-half years as the winning percentage approaches .700.

The Age graph, though flatter, expresses the slightly curvilinear arc that Experience did. At a .400 winning percentage, the average age approaches 28. It then holds steady between 28 and 29 until a .625 winning percentage. Again the above-.500 teams are slightly older (maybe by a half year). Above .625, the age drops quickly to between 27 and 28 (this may be due to the smaller sample size being heavily influenced by younger, nineteenth-century teams).

Finally, the debut age is the flattest of the lot, holding steady around 23 throughout. There is a slight age bump (to just under 24) with winning percentages under .375. Above .625, the graph dips close to 22. However, in both cases as the percentage gets more extremely, the graph returns to the norm (23).

So if there is any relationship, it's not very strong. If you're building a team for this year, just get the best players available regardless of age and experience.

Rookie Performance:

Finally, here's a rundown of how well rookies perform by decade, split up into batting and pitching. In each case, the typical statistics for all rookies are derived and then they are normalized by the major-league average (a la Baseball Reference's OPS+, though with no compensation for ballpark).

First let's look at some general numbers for all players:

DecadeAvg Wt ExpAvg Wt AgeAge-Exp
1870s2.04724.84122.794
1880s3.53626.17722.641
1890s5.01827.49222.475
1900s4.76528.20023.436
1910s4.38227.21622.834
1920s5.33628.34323.006
1930s5.06528.38723.322
1940s4.65728.70424.047
1950s4.75728.45423.697
1960s5.02427.66422.640
1970s5.53727.58622.049
1980s6.03428.53822.504
1990s5.53328.67023.137
2000s5.88929.19423.304

You'll not that players are getting older and more experienced, and that their "debut age" is getting higher even as analysts claim that players are getting rushed to the majors. Also, the Forties stand out as the only decade with a debut age over 24, clearly being greatly affected by the dearth of talent during World War II. The Sixties, the first decade of expansion and of the amateur draft, saw debut ages drop dramatically. As the leagues stabilized in the Eighties, the experience went up, but it took more hits in the last two decades probably due to two more rounds of expansion (and potentially more foreign-born players in the majors).

Now let's look at the batters. First, here are some basic demographic numbers (Age+ is the average rookie age normalized for all players):

DecadeAvg AgeAge+%Rookie%AB
1870s22.73504279241%23%
1880s22.79089799031%14%
1890s23.28552468826%10%
1900s23.9322828828%11%
1910s23.05177998827%8%
1920s23.98921168724%8%
1930s23.95761088621%8%
1940s24.57448638721%9%
1950s24.06542068619%8%
1960s22.86970428518%5%
1970s22.92325238515%4%
1980s23.66803848515%5%
1990s24.17136778617%5%
2000s24.40684418616%4%
Total23.63712258620%7%

You'll notice that rookies have been getting older for the past five decades even though the disparity between rookie and veteran players holds steady (Age+ of 85-86). Also, teams have consisted of fewer rookies and they have gotten a smaller percentage of the at-bats since the Sixties.

Now here are the average and normalized rookie batting statistics:

DecadeBABAOBPOBP+SLUGSLUG+OPSOPS+
1870s.25294.26895.31895.58595
1880s.22891.26288.29989.56188
1890s.24990.31792.32789.64590
1900s.23292.28792.29289.57991
1910s.22588.28990.29186.58088
1920s.26793.32493.36592.68993
1930s.26194.32093.37093.68993
1940s.24895.31194.33290.64392
1950s.24193.30492.34789.65190
1960s.22791.28791.32286.60988
1970s.24094.29892.32586.62489
1980s.24394.29992.35090.65091
1990s.24291.30291.35186.65488
2000s.24893.30691.37889.68490
Total.24292.29891.33187.62989

And:

DecadeAB/HRAB/HR+SB%SB%+K/ABK/AB+
1870s428.29474.90%1080.045122
1880s230.3236140100.00%1000.059104
1890s182.6925131100.00%1000.067130
1900s341.4043140100.00%1000.000N/A
1910s283.16814689.21%1010.119126
1920s106.970112558.81%980.112137
1930s75.7603411876.95%1060.121127
1940s104.614316074.12%1030.120116
1950s58.3367514461.06%1030.157122
1960s64.5217915661.58%990.205122
1970s83.7088618462.86%980.176116
1980s56.8175413566.42%980.190120
1990s54.0661515168.47%1000.217121
2000s43.2840613968.97%1000.220116
Total95.1877217278.57%1030.124103

Well, gee, rookies really stink. Aside from stolen base percentage, they just are not very good at all. Let's see if the pitchers fare better…

Here are the demographic data for rookie pitchers:

DecadeAvg AgeAge+%Rookie%IP
1870s22.019138%25%
1880s22.099134%21%
1890s22.789131%15%
1900s23.629032%13%
1910s22.918930%10%
1920s24.048826%9%
1930s24.168622%9%
1940s24.828722%10%
1950s24.238721%9%
1960s22.938520%8%
1970s22.928517%7%
1980s23.858617%7%
1990s24.308719%9%
2000s24.358618%9%
Total23.668722%10%


The trends that we saw with the batters are evident here, but teams do seem slightly more willing to devote innings to rookie pitchers, at least more so than they commit at-bats to rookie batters.

Here are the rookie pitching stats (Note sub-100 normalized data represent worse than average values throughout):

DecadeERAERA+WHIPWHIP+K/BBK/BB+K/9IPK/9IP+R/9 IPR/9IP+
1870s3.46821.38911.28701.1988N/AN/A
1880s3.59911.33951.55903.841016.4288
1890s4.47911.56960.75942.891056.7391
1900s3.30861.35921.11803.38954.7985
1910s3.48851.40911.01803.68994.7184
1920s4.58881.55930.72772.74975.4988
1930s4.71911.56930.82803.371005.5191
1940s4.12911.47950.83833.43964.7591
1950s4.37911.48941.03844.501014.9491
1960s3.83931.38941.44795.731004.3593
1970s4.00921.41951.34865.09994.4993
1980s4.15931.41951.45875.29984.6194
1990s4.78901.49941.49835.95965.2490
2000s4.92911.49941.54816.33975.3591
Total4.12921.44941.17824.27945.1089

That's not much more encouraging than the rookie batting stats. Again aside from one stat (Strikeouts per nine innings), the rookie pitchers are considerably worse than average.

It's no wonder teams have been eschewing rookies for veterans over the past five decades, right? That's why GMs are more willing to employ Wil Cordero and Jose Offerman rather than promote from within.

Well, that's the simplistic conclusion. Yes, rookies are on average worse than veterans. However, that doesn't mean every rookie will destroy your staff or become a sinkhole in your lineup. It also doesn't mean that every retread will salvage your team. It just means that GMs have to be a bit more discerning when it comes to the rookies they promote. Many will excel, but the GM will have to do his homework. It just seems that GMs historically (at least over the past five decades) have been more willing to take the easier route and just rely on a retread with a lengthy resume so that he'll have something to point to when they eventually fail.

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