I went off script a couple times during a recent sketch show. In one instance, I responded to an unexpected event during the performance (a hanger fell) before returning to the main dialogue. In the other, I tried something out during a rehearsal and cleared it with both the sketch’s writer and fellow performers before repeating the line during the actual show.
I’ve attended workshops that give advice on how to improvise a sketch via the pattern game, but one of my favorite things about performing sketch is finding those moments of improvisation in a piece that’s already been written. According to Wikipedia, the history of improvisation in sketch is at least as old as commedia dell’arte, which often mixed well known plots, scenarios, and sketches with improvised characters.
I take this to heart when memorizing lines and often start by memorizing the emotional reactions and behavior patterns of my character during the course of sketch, letting myself converge to the lines after running the sketch a few times with the other actors in it. The technique doesn’t always work, particularly in sketches that are contingent on word play or the execution of specific lines of dialogue for a joke to land– Thomas Middleditch talks about this in an interview— but when it does, it becomes easier to play the scene and recover in those instances when something doesn’t go according to plan.
Because sketch creates an expectation for other performers on how the scene will unfold, it’s important to be mindful of how improvisation in sketch affects others. For instance, a last-minute change can cause another performer to break. Likewise, one needs to take into account that sketch often starts from the vision of a writer. An improvised line might be funny but could potentially alter what the sketch writer intended. There have been moments in which I had an idea for a line during a performance but chose not to because of how others might react. Still, under the right circumstances, as with the case of Bill Hader’s Stefon character on Saturday Night Live, causing another performer to break or derailing the sketch can also be the goal.