ABSTRACT
The R system is well-suited for fitting statistical models to data. One popular topic in sabermetrics is the rise and fall of a player's season batting, fielding, or pitching statistics from his MLB debut to retirement. This chapter discusses a famous career trajectory. Mickey Mantle made an immediate impact on the New York Yankees at age 19 and quickly matured into one of the best hitters in baseball. It presents the computation of many fitted trajectories to compare career performances of similar players, it is helpful to contrast their trajectories. A general problem focuses on a player's peak age. The chapter looks at the fitted trajectories of all hitters with at least 2000 career at-bats. It explores the pattern of peak ages across eras and as a function of the number of career at-bats. The chapter focuses on the period 1985-1995 and contrasts the peak ages for players who play different fielding positions.
