My friends ______ football at the moment.

The subject is "My friends", which is plural. Therefore, the plural form of the verb "to be" is required. The options are "is playing", "are playing", and "am playing". "Am playing" is used with "I". "Is playing" is used with singular subjects. "Are playing" is used with plural subjects. Thus, "are playing" is the correct choice to agree with "My friends".

The correct answer is: are playing