put one off stride
put (one) off (one's) stride
To disturb, distract from, or interfere with what one is doing, such that they are unable to do it well. It really put me off my stride to have my parents watching while I worked on my painting. The boxer tried to put his opponent off his stride by getting in his face right before the fight.
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
put one off one's stride
1. Lit. to cause one to deviate from a rhythmic stride while walking, running, or marching. A rabbit ran across the path and put me off my stride.
2. Fig. to interfere with one's normal and natural progress or rate of progress. Your startling comments put Larry off his stride for a moment. He was put off his stride by an interruption from the audience.
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs. © 2002 by The McGraw-Hill Companies, Inc.