What makes a prospect successful?

My brother Andrew and I were recently having a discussion about prospects, and whether or not left handed hitting prospects struggled more than right handed hitters. Mike Moustakas' difficulties against left handed hitters worried Andrew, and even managed to conjure up the ghost of Alex Gordon. His thinking was that right handed hitters have to learn how to hit right handed pitchers, otherwise they wouldn't succeed, even in the minors. Left handed hitters, on the other hand, couldget by without learning to hit left handed pitching. There is also fewer quality left handed pitching in the minors, particularly when it comes to velocity, and when suddenly exposed to major league lefties, a left handed prospect could struggle.

I established my prospect pool using Baseball America's top 25 rankings from 1995-2005. I only went up to 2005 to ensure that any top 25 prospects had a chance to become established major league players. Because our original discussion focused on top prospects like Alex Gordon and Mike Moustakas, I only selected the top 25. Once pitchers were excluded and the list was pared down to account for players appearing in multiple years, I was left with a total of 109 batters - 59 righties, 37 lefties, and 13 switch hitters.

To measure their success in the majors, I went with Wins Above Replacement (WAR), which is readily available from Fangraphs. Although these values include defense, I didn't want to exclude defense entirely, as a prospect may have made the list based on their defensive value. If, for example, right handed hitters have more of their value in defense because all shortstops are right handed, this difference could incorrectly be attributed to some difference in the hitting of prospects. I looked at WAR three different ways - the average annual WAR for their career, the WAR for their best year, and the total WAR accumulated for their career. I considered a major league career to have started the first season the player had at least 100 at bats, to reduce the impact of "cups of coffee", particularly on average WAR. Here are the average values.

Handedness		WAR
	Count	Average	Peak	Total
Left	37	1.75	4.13	15.98
Right	59	1.59	3.59	17.48
Switch	13	3.20	5.22	28.82

As you can see, there is not much of a difference between left handed and right handed prospects. Interestingly, top prospects who are switch hitters seem to have a much higher rate of success than either right handed or left handed batters. To see if extreme examples influence the averages, we need to look at the breakdown of successful players. I categorized players by average WAR for their career, and defined anyone with an average WAR of less than zero as a washout, between zero and one as a scrub, one to three as a starter, and anyone who average WAR of greater than 3 as a star. Some examples, Nomar Garciaparra and Miguel Tejada are just on the star side of the starter/star threshold, thanks to some poor decline years for both. Players who easily end up in the star category should be familiar to any baseball fan – Carlos Beltran, Alex Rodriguez, and David Wright. Starters include players like Johnny Damon, Darren Erstad, Carlos Pena, and BJ Upton. Scrubs are players like Jay Payton, Jeff Francouer, Wilson Betemit, and Todd Walker - although they've started and succeeded for a couple years in their career, for the most part they are bench players. Washouts either never made it, like Drew Henson, or were terrible in the big leagues, like Andy Marte.

	Washout	Scrub	Starter	Star
Avg. WAR	<0	0-1.5	1.5-3	3+
Left	14%	41%	27%	19%
Right	25%	34%	22%	19%
Switch	0%	23%	23%	54%

Again, we see no major differences between left handers and right handers, but top prospect switch hitters have an incredible track record. The sample size is very small (n=13), but top tier prospects that are switch hitters have an incredible track record.

Of course, I would be completely remiss if I didn't actually run any statistics to see if these perceived differences were borne out. After all, I'd definitely dock my students a few points for saying, "See! They're different!" without any statistical support.

Warning! Stats ahead!
An analysis of variance (ANOVA) is the quick and easy way to tell if the handedness of a batter impacts any of the WAR measurements we used. Handedness was not a significant predictor for either total WAR or peak WAR (p=0.16 and 0.14 respectively, where a difference is significant if p is less than 0.05). Once we know that there is a significant effect of handedness on average WAR, we can use a Tukey's Honestly Significant Difference Test, which shows that switch hitters in Baseball America's top 25 prospects have significantly better results than left handed or right handed hitters, but there is no difference between left handed and right handed hitters.
End of Stats

Now that you've made it through the statistics (or skimmed, don't worry, there won't be a quiz at the end), we can take a look at the pretty pictures instead!


A quick refresher on box plots: the line in the middle of the box is the median for the group. The top and bottom of the box are the 75th and 25th percentile, respectively (also called the first and third quartile) and the lines represent the range of the remaining data. Outliers are shown as small circles, but there is only one - Alex Rodriguez and his average of 6.75 wins above replacement. I like to imagine that little circle looking down on everyone else while being fed popcorn, just like at the Super Bowl!

So what exactly does this all mean for prospects? Are switch hitting prospects more likely to succeed? It is one possible explanation, but it certainly isn't proven with this analysis. One alternative explanation is that for a switch hitter to be listed in Baseball America's top 25, they have to be pretty damn good. Switch hitters often first start switch hitting in high school or later, so the non-dominant side can lag behind in development. Perhaps if a switch hitter is playing well enough to make Baseball America's top 25, they're already a fairly polished player.

Either way, a switch hitter on the top prospect list seems to have a great shot at becoming an impact player. In the last two years there have only been three switch hitters in the top 25 – Carlos Santana, Justin Smoak, and Aaron Hicks. I'm sure this article is a small consolation to the Mariners and their fans after the Cliff Lee trade, when they ended up with the switch hitter Justin Smoak (BA's #13 prospect for 2010 season) who struggled mightily in Seattle instead of right handed Jesus Montero (#4 in 2010, #3 in 2011).

Let me know if you have any other questions that might be answerable using this database. A comparison study using pitchers would be an interesting follow up, as would expanding the prospect pool to the top 50 or beyond.