There are free football pitches between living areas like for example @Al Bada'a area has an empty ground with two goals on it's sides. Not really a football pitch but can do the job. It's more of a beach football with all the sand.
Other living areas might have better football pitches as i heard
@Al Qusais area has one.
Or you can contact schools and book their football pitches but that would be for money not free.