http://dictionary.reference.com/search?q=sidetrack&x=37&y=8
Here’s a Word of the Moment that’s commonly used, but whose origins I had never before considered:
Sidetrack , v.
1. to move from the main track to a siding, as a train.
2. to move or distract from the main subject or course.
[Origin: 1825-35, Americanism]