The scene starts. Your improv partner runs on, and says to you, “Nice shirt.” You immediately retort, “I’m not wearing a shirt!” That’s a block, and can be a common thing among beginner improvisers to do.
Blocking is negating the ideas, suggestions or actions of people around you (or possibly even yourself) and can often result in a stalled scene. Blocking is a rejection of the reality that is presented in the scene. Blocking is often the opposite of saying yes… and.
How to avoid it? Be present in the scene. Don’t be focused on what you are going to say, and especially don’t be focused on saying the most outrageous thing because you think it’s funny. The act of blocking isn’t what can make a scene go still, it’s how everyone reacts to that block. If you’re blocked, or you block someone, don’t shut down. Maybe that block is the new shift of the presented reality needed to make the scene hilarious. Shifting, and being adaptable to what is thrown at you on stage is an essential part of improv comedy.