It is experimental (aka empirical) because its based on prior data recorded from past games of the current season or prior seasons. Empirical probability is always based on past data. Another example is let's say you flipped a coin 10 times and got 4 tails, so that means the empirical probability of getting tails is 4/10 = 0.4. The theoretical probability is 0.5 if its assumed each side is equally likely to be landed on.
