"Go out and play."
Translation:Sai e vai jogar.
To me the 'vai' helps indicate the sequence in which the actions should be done.
If you only wanted to use the verb "jogar" (in a lesson not designed to practice using the simple future), you would also have to conjugate "jogar" to the second person singular informal form (the 'tu form') of the imperative: "sai e joga!"
The sentence uses the 'tu' form for both "sai" (from "sair") and "vai" (from "ir"). At first it is a little confusing, that the 'tu form' of the imperative is written the same as the third person singular present. http://www.conjuga-me.net/verbo-ir