chapter 1 illustrated the changes of baseball team performance over the history of baseball, but interesting patterns in performance exist over time when viewed at the individual level. Generally a professional athlete enters the professional ranks at a modest level, increases his or her level of performance until a peak level is reached, and then decreases in performance until retirement. When some measure of performance is graphed against age, this graphical display is called the career trajectory of the athlete. Although the general “rise, hit a peak, and then fall” career trajectory pattern happens in all sports, the characteristics of this pattern can vary. For example, some athletes may peak at a younger or older age, and the rise and fall from peak performance can occur at different rates.