Sentence:  "Oh," they yelled, "you could, eh? Well, let's see you do it, then! Let's see you do it! Let's see you do it! Now!" In a moment the crew of little spectators were gibing at Horace. The blow that would make Jimmie's humiliation complete! Instead, it had <WSD>boomeranged</WSD> Horace into the mud. 
Meaning of the word marked with <WSD> tags:  To return or rebound unexpectedly, especially when the result is undesired; to backfire.