In athletic training, it’s vitally important to define, exactly, what you are attempting to achieve out of an exercise program.  Just “lifting weight” and running will not produce the same results as a structured exercise regimine designed to attain a specific goal.
With that said, one of the main misconceptions in athletic training is the distinction between strength training and power training.
Without going into deep detail, the force-velocity curve is a graph that illustrates that as force production goes up, speed will go down.  For example, an athlete maxing out with a 1 rep 315 pound bench press is creating a lot of force, but very little speed.  If that same athlete dropped the weight to 185 and pressed with max effort, the total force would be less (dictated by the smaller weight) but the speed of the movement would rise dramatically.
Power production is a key component to almost all sports, especially basketball, volleyball, football, baseball, golf, tennis and many more.  To train your body to move powerfully on the field or diamond or court, you have to train that muscle with high velocity in the weight room. 
To be clear, strength is an important element in these sports as well, but a year-round strength training program with low regard to power with leave an athlete performing below their potential during the season.
A perfect example is the ever-popular “big four” lifts seen so often in high school weight rooms.  The big four consists of the barbell deadlift, barbell squat, barbell power clean, and the barbell bench press.  These exercises are typically performed with 1-5 reps. Besides for being a non-functional way of training for athletics, these slow grinding movements with max weight DO NOT train an athlete to move powerfully.  The athlete may be able to move a mountain from a to b, slowly, but they won’t be trained to move quickly (which is generally the more important aspect of most sports).
Make sure you understand what your training regimine is attempting to achieve, and time-out the program so that you are moving optimally with speed just before the season so you can realize the benefits of those changes when it most matters.
Matt Pirtle, MA, CSCS
Emerge Fitness Training