The Changing Look of MLB Rookies

One (admittedly very subjective and non-scientific, but interesting) way to gauge quality of player is to look at the demographics of the players that are entering the league. Below, we’ll look at a variety of statistics related to players in their rookie year (which we are considering the year that they made their MLB debut, regardless of the number of games played).

A good statistic to start with is how long the players spent in the minor leagues.

(Original post explaining the project goal here and the project code for this post is here. All data scraped from www.thebaseballcube.com and the web scrape code is here.)

Domain Context

To understand why this is a meaningful statistic, we’ll take a brief detour to understand the stages of Major League Baseball. Unlike the NBA, where players largely go straight from the draft to the league, MLB has an intricate minor league system that develops and prepares players before joining the professional team. The steps before the Major League team are known as the “Minors”.

The Minors consists of leagues such as A (“Single-A”), AA (“Double-A”), AAA (you get the pattern by now…), with AAA being closest to the majors. During this time, the player receives instructional teaching from a variety of coaches specific to their position. Teams look to the quality of their Minor League system both as an indication of future success and as an opportunity to improve their professional team via trades of up-and-coming prospects for established professional talent.

A Minor League career can be as little as under a year (rare) or as long as a whole career. Some time, but not too long, in the minors is generally recognized as prudent. There are a few different interpretations that could be taken from a change in data.

Longer trended time in the minors could mean there are fewer strong players in the pipeline for teams, and therefore they need more time for development and aren’t “Major League ready”. Alternatively, some may say a rookie is more prepared for the league because of the fact that they’ve received more training.

Ultimately, the interpretation is player-specific, and we will explore whether the value is changing and in which direction it has trended.

What does the data say?

After removing some bad data, we get the following plot for the average length of time to reach the majors. Unsurprisingly, the data is centered on 3–5 years and has a long tail that extends as far as 16 years.

While unusual, it’s not unheard of to see players that reach the major leagues quickly. They could have been signed out of a professional league in another country or may just represent the best of the best. To validate this, we can look at their data compared to the overall player set.

The over-performers — those that reached the major leagues in a year or less — were, on average, drafted in the 4th round, while the average for all players that reach the MLB was the 9th round. In tandem, their average pick number was 92.6 compared to 258 (Note: Lower values for draft round and pick number are better). They also lasted an average of 7.62 years in the Major Leagues compared to 5.30 years for all players.

What’s the trend?

The logical next step is to understand how this number has trended over time. The chart below shows the average time to reach the majors for rookies entering the league from 1960–2017 (2018 was excluded because the data is not final yet). We see that the time to reach the majors has steadily risen since 2011 and is currently at an all-time high of more than 5 years for players that debuted in 2017. The average number of years to reach the majors has increased 10%+ from 2010–2017.

Another way to look at this data is how it distributes each year. So as not to clutter the plot too much, we’ll filter the data for only 1990-Present, since this is the timeframe that matches the weather analysis previously conducted. Below, we can see the distribution of values has become tighter on both the bottom and top end of the spectrum. In addition, the median value is near the higher end of the time period, and has stayed consistent over the past 4 years.

One possible interpretation is that there are less superstars coming up through the league (as evidenced by the low number of “outlier” players entering the league in less than a year). Also, with the higher median value, this could indicate that players need more development prior to entering the league. Again, there are a number of possible explanations, and the above is just speculation, but it does appear the last 3–4 years have shown different activity relative to the prior decade.

Rookies per year

Another metric we can look at to gauge quality of play on the field is the average number of rookies per team, with the idea being that more experienced players would provide a better quality of game on the field. From the chart below, we can see a lot of noise in the data as the average number of rookies per team fluctuates from as low as 4 to as high as 9. That said, it looks like we’re on an upward trend recently.

A final stat that we can look at is how the percentage of rookies in the league that are undrafted free agents has changed. Again, this doesn’t necessarily speak to quality of player (it maybe says more about the quality of scouting) but is still an interesting chart worth looking at. Overall, we see the trend moving between 15%-30%, though exhibiting a somewhat upward trend over time, with the current number near the all-time high reached in the mid-2000’s.

Conclusion: What did we learn?

Looking at charts and graphs can each individually tell an interesting story, but good data analysis brings together the charts into a cohesive story.

One interpretation of the data is that — absent commentary on the players individually — the type of player entering the league is different. They are spending more time in the minor leagues (and subsequently entering the majors at an older age), the length of average career is on a moderate downward trend, and as a result the number of rookies per team on average is increasing. Finally, undrafted free agents as a percentage of rookies is demonstrating an upward trend.

As the sport has faced declining interest over the past decade, it’s very possible that the athlete who historically chose to focus on baseball in high school or beyond is now choosing basketball, football, or even soccer. As the years pass and more of those “missed players” do not filter upward through the amateur draft and college ranks, those that are left may need more time for development to reach Major League potential.

A few readers have even commented on looking at participation in Little League as a leading indicator of the future popularity of the sport, and I completely agree. The quality of the product is only as good as the players that choose to play the sport, and that starts at a young age.

Again, the underlying drivers and implications that I’ve outlined above are inherently speculative. Having said that, the problem is backed by hard data, even if my interpretation is off. MLB would be prudent to approach the challenge from multiple perspectives, with the ultimate hope that improving the on-field product will result in reversing the stagnating popularity of the sport.

Coming up next…we’ll analyze data from historical final standings of MLB teams to look for changes in the nature of competition as it relates to the distribution of talent in the league.