Unlike novels, which can be written in a variety of tenses, screenplays are always written in present tense.
Some writers employ an objective 2nd person tense for point of view, where “we” stands in for the audience.
Through the crowd of befuddled heads, we see a MAN IN HORNED-RIMMED GLASSES, staring with intent.
The present progressive can also be a valuable tool, as it is a way to express ongoing — and therefore interruptible — action.
Ryan is cutting the lawn, rocking out to his iPod, oblivious to the world around him, when the kids’ baseball PLUNKS him in the head.