Corey Seager, the 2016 Rookie of The Year, LAD All-Star SS finished 3rd in the MVP race. At 22 years old, Seager has played in 184 Major League games accumulating a .312 BA in 725 at-bats.
Trea Turner, the Nationals rising star, also has had an incredible start to his career capturing 8 triples and 35 stolen bases in 100 games. In nearly half the at-bats, 347, Turner holds a .329 batting average.
So who has gotten off to the better start? Seager sports an OPS of .892, while Turner carries a .900. We'll predict their Career Batting Average based on their At-Bats thus far.
David Robinson’s website, varianceexplained.org, gave me this idea. His blog is extremely resourceful and gave me the idea of using a beta distribution to compare MLB players since baseball is a game of "hit or miss". One post, Robinson explains what a beta distribution is and an example using batting average. In his words,
“In short, the beta distribution can be understood as representing a probability distribution of probabilities- that is, it represents all the possible values of a probability when we don’t know what that probability is.
Here is my favorite explanation of this: Anyone who follows baseball is familiar with batting averages- simply the number of times a player gets a base hit divided by the number of times he goes up at bat (so it’s just a percentage between 0 and 1). .266 is in general considered an average batting average, while .300 is considered an excellent one.”
Later in the post, Robinson figured the distribution for the MLB should lie between (.2, .35) and have a mean of .270. Meaning the majority of hitters will hit .270 a few bad hitters will hit .200 and a few superb hitters will hit .350. By trial and error Robinson found the correct parameters (alpha and beta) to reasonably represent the beta distribution of players in the MLB. This is represented as such:
alpha / (alpha + beta) = .270
alpha is a success (hit) and beta is a failure (out)
alpha = 81; beta = 219
81/(81+219) = .270
So if the average player is going to hit .270, this led me to wondering whose batting average has been more impressive Seager or Turner thus far?
We can’t solely look at average since Seager has twice as many ABs as Turner. So I simply added Seager’s hits to alpha and his outs to beta. Then did the same with Turner.
Green: Trea Turner distribution
Blue: Corey Seager distribution
Red: Distribution of MLB Batting Average (minimum hit a .200, maximum hit .350)
In conclusion, although Turner has hit .17 points better than Seager to date, their averages have been equally impressive compared to the rest of the league. Both are excellent hitters and are expected to hover around .300 for their career. Since Seager has 378 more at-bats than Turner, Seager’s distribution is slimmer than Turner’s. We are more confident in predicting Seager’s batting average because he has more at-bats. Turner, hit .342 last year in an abbreviated season. This distribution gives him about the same chance to hit .280 as .342 this upcoming year. It’ll be interesting to see how Turner and Seager will compare next season.
Turner Predicted Batting Average: .301
Seager Predicted Batting Average: .300
UPDATE: May 12th, 2017
Around a fifth of the 2017 season has passed, lets look at the updated predicted batting averages of Trea Turner's and Corey Seager's. Both are hitting below their career average to start out the 2017 season:
Turner is 26/100 or .260
Seager is 36/126 or .286.
Green: Trea Turner distribution
Blue: Corey Seager distribution
Red: Distribution of MLB Batting Average (minimum hit a .200, maximum hit .350)
Turner Predicted Batting Average: .296
Seager Predicted Batting Average: .298
Turner's poor start to the season has resulted in a .05 drop in the Predicted Batting Average in just 100 At-Bats. It'll be interesting to see if Turner will turn around his slow start and where the Predicted Batting Average will confine to with more at-bats. Interestingly, Turner bats .05 points higher than Seager for his career, but our Predicted Batting Average favors Seager slightly.
Turner Career Batting Average: .313
Seager Career Batting Average: .308