If something - particularly an idea or a suggestion - is described as 'off the wall', it is shocking or unusual. The origin of this expression comes from sports like handball, racquetball or squash, in which the ball is hit against a wall. When the ball comes 'off the wall', the player is uncertain where it will go. Therefore, an 'off the wall' idea is a rather unusual idea, and no one is entirely sure where it will lead. In other words, the outcome is unpredictable!
"This movie is strange. It's really off the wall."
"Simon had some really off the wall ideas on how the department should be run."
