Main Variables: sum of free throws attempted, sum of free throws made, average free throw percentage.

Control variables: height, number of players per height category

Value Ranges: heights: 5-9, 5-11, 6-0, 6-1, 6-2, 6-3, 6-4, 6-5, 6-6, 6-7, 6-8, 6-9, 6-10, 6-11, 7-0, 7-1, 7-2

Data Source: http://stats.nba.com/

Research question: In the NBA, can height predict free throw shooting ability?

From your information above it appears you have one independent variable and three dependent variables.  You want to have only one dependent variable and numerous independent variables.

A better question may be “Is there a relationship between height and free throw statistics?” You could then use height as the dependent variable.  Your three categories can be the independent variable 1. sum of free throws attempted,  2. sum of free throws made, 3. average free throw percentage as three different independent variables.  This will determine if there is a relationship between various free throw stats and height.   

You will want to run an individual regression model on each independent variable and then one combined multiple regression model.