Methods that return the highest score from the list

[Larz60+]

It's all one program. It's fine if not combined into a class, but the rules are a bit different.
Things have to defined before being used.

The gamePlayersList error is fixed, the f error is a new error.
since python is interpreted, you only see errors as they are encountered.
The error you are getting now is because you are trying to use f before it's defined:

hree_highest_scores(max(gamePlayersList), max(f), max(x))

you are mixed up on what goes where.

a, b, and c are attributes of the function Three_highest_scores. Inputs if you will, not outputs.

for outputs, you return values, which can be modified input values
you are trying to assign values to the input arguments of the function from within the function, that's now how it's done.
consider the following:

def ziggy(a, b):
    return a + b

print(ziggy(2, 4))

output:

Output:
6

a and b are input arguments, you must supply these values
the function adds a and b and returns the result