Evaluating Minor League BABIP

In recent years, baseball fans have had something of a complicated relationship with BABIP, or Batting Average on Balls in Play. Simply put, BABIP measures how often a batter ends up with a hit after putting a ball in play. It's generally believed that a hitter's BABIP will tend to regress toward .300 - at least at the major league level.

Problems can occur, however, when we try to apply that thinking to prospects in the minor leagues. Often, when looking at a player's stat line, I will see someone conclude that the player may not be as good as their numbers suggest, because their BABIP is much higher than average. The thinking goes that if the player's BABIP was at a more "reasonable" number, as would be expected in the major leagues, then the player wouldn't have performed as well.

I've long suspected that there is a flaw in this method of thinking. Namely, a player can carry a high BABIP through the minors for several reasons: Defenses are not as crisp in the minor leagues. Playing surfaces are not as polished. Maybe he's a right-handed batter who pulls a lot of grounders, putting pressure on inferior third basemen. Maybe.

Speedy players also tend to carry high BABIPs, even at the major league level, because they can beat out more grounders. We expect this to happen even more often in the minors, where infielders are not as good. We also expect more fly balls to land for base hits because the outfielders are not as good.

But intuitively, I believe the likeliest reason that a hitter might carry a high BABIP in the minors is because he's better than everybody else.

Let me explain. BABIP tends to be highly influenced by batted ball types. Line drives create the highest BABIP, followed by ground balls, and finally by fly balls. A line drive is generally achieved by a batter "squaring up" a ball.

In other words, if a hitter is consistently better than the pitchers he faces, he should be expected to "beat them" more often, resulting in hitting more line drives and, consequently, end up on base on more of his balls in play.

All-Stars

I cannot state enough that I am neither a great statistician nor a great mathematician. I don't know my SQL from my SOL. If you're looking for a deep dive into the numbers here, I wish I could provide it, but I simply can't.

So to test my theory, I had to rely on what I could do. I took a look at every player who was named to at least two All-Star teams between 2010 and 2015 (I chose players who served on two to try to weed out as many players as possible who were only All-Stars to satisfy the one-player-per-team requirement.)

I took each of these fifty-five players and went back into their minor league careers, comparing their BABIPs at Single-A, High-A, Double-A, and Triple-A to their peers. This is what I discovered:

• Single-A: +.027
• High-A: +.028
• Double-A: +.031
• Triple-A: +.026

As a group, the All-Stars consistently out-performed their peers in terms of BABIP as minor leaguers. This was not exclusive to speedy hitters, either. David Ortiz, Joe Mauer, and Matt Wieters were all among the players with the widest average discrepancy between personal BABIP and league BABIP over the course of their minor league careers:

1. Mike Trout (+.089)
   
2. Jay Bruce (+.073)
3. Derek Jeter (+.072)
4. Rafael Furcal (+.071)
5. David Ortiz (+.069)
6. Jose Altuve (+.064)
7. Matt Wieters (+.062)
8. Starlin Castro (+.059)
9. Justin Upton (+.057)
10. Michael Bourn (+.052)
    Joe Mauer (+.052)

(These numbers are the average point differential between all four full-season minor league levels.)

This is a good sign that elite hitters tend to carry high BABIPs through the minors, but there were some examples of players who actually under-performed their peers through the minor leagues:

1. Salvador Perez (-.019)
2. Troy Tulowitzki (-.017)
3. Manny Machado (-.014)
   Paul Konerko (-.014)
5. Josh Donaldson (-.013)
   Brian McCann (-.013)
7. Adrian Gonzalez (-.005)
   
8. Robinson Cano (-.003)
9. Yadier Molina (-.001)

In fact, with the exception of Perez (Triple-A,) McCann (Single-A,) and Gonzalez (Single-A,) none of these players exceeded their league's BABIP at any individual level.

Looking at the list, we can understand many of them. Perez, McCann, and Molina were generally regarded as glove-first catchers. Donaldson was a late bloomer. Gonzalez was considered something of a bust until he went to San Diego. But Cano, Machado, Konerko, and Tulowitzki were always considered pretty good hitters.

Still, the evidence suggests that truly elite hitters tend to over-perform their minor league peers in terms of minor league BABIP.

General Population

It's all well and good to look at the best hitters in the game, but what about the general population of prospects?

I looked at the Single-A, High-A, Double-A, and Triple-A seasons from 2006-15 and looked at every hitter who had at least one hundred plate appearances in each individual season.

Rather than try to individually ascertain which players were "prospects," I let the teams determine this for themselves. Teams tend to promote their better players fairly aggressively. The youngest players in a given league tend to be among the best players, as teams tend to challenge their most-promising players.

So what I did was I grouped the players by age. First, I looked at the youngest 25% of players, followed by the youngest 13%. This is what I found:

Single-A BABIP by Year: 2006-2015

It shouldn't be surprising that Single-A doesn't give us anything definitive. I have two working theories for this: First, this is a player's first experience with full-season ball, and teams haven't yet determined who the most-promising hitters are. Second, the age disparity between the youngest and the oldest players is not all that significant in Single-A. Third, even if the youngest players were the best prospects, they're really still learning how to hit professional pitching.

But as we get closer and closer to the majors, a trend develops:

High-A BABIP by Year: 2006-2015

Double-A BABIP by Year: 2006-2015

Triple-A BABIP by Year: 2006-2015

The closer players get to the major leagues, the better the younger players are at getting hits out of the balls they put in play. Is this a coincidence? I don't think so. More likely, it points to the fact that minor league BABIP can serve as a pretty strong indicator of talent level.

Conclusions

Minor league BABIP isn't a magic salve. After all, Adrian Gonzalez has a 131 career wRC+, but never had a higher-than-average BABIP in the minors. Meanwhile, DJ LeMahieu consistently out-performed his league BABIP, but has carried a career wRC+ of 75 in the majors.

But for the vast majority of players, carrying a consistently-high BABIP in the minors - particularly for a young player - actually seems to be a decent indicator of future success as a hitter.

There are a handful of players in the Astros system who, despite being young for their level, have put up consistently-high BABIPs. Alfredo Gonzalez, who was recently put on the Astros' 40-man roster in advance of the Rule 5 Draft, has put together high BABIPs at all of his full-season stops despite being young for the level. Ditto Colin Moran, who many believe to be on the Astros' fast-track list for the majors. Ditto Nolan Fontana, also added the Astros' 40-man roster.

I do not want to overstate the importance of BABIP. As we've seen, some players are very good major league hitters without having it in the minors, and some players are mediocre major league hitters despite having it in the minors. But I do believe that rather than dismissing players' numbers and expecting regression from high BABIPs, it should be viewed as one more piece to evaluate when looking at true talent level, because good young hitters should - more often than their peers - beat mediocre pitchers.