off-the-wall

• off the wall

Perhaps from baseball or other games played with a ball, alluding to unpredictable bounces; but compare also bounce off the walls.

• Audio (General Australian):

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off-the-wall (comparative more off-the-wall, superlative most off-the-wall)

1. (idiomatic) Wildly unconventional; bizarre; absurd.

   What kind of a harebrained, off-the-wall idea is that?

   She is a very off-the-wall character.

   • 2015 March 19, Alessandra Stanley, “'Empire' Finale Review: A Sizzling End to Season One”, in New York Times‎^[1]:

     What makes it surprising, though, are the glimmers of wit and self-awareness beneath all the rap star swagger and over-the-top confrontations. Even the fervid finale had a few off-the-wall side jokes.

2. (idiomatic) Of a person's behaviour: greatly inappropriate.
   • 2012, Reginald Pierce, The Paladin, page 204:

     All of their friends were amazed that they were familiar with a war hero. Some began to understand Chips' moods and drinking. His "off the wall" behaviour at times. And unknowingly they were "forgiving" him.