jump the track

[jump the track] {v. phr.} 1. To go off rails; go or run the wrongway.

The train jumped the track and there was a terrible accident.

The pulley of the clothesline jumped the track and Mother's washingfell down.

2. {informal} To change from one thought or idea toanother without plan or reason; change the thought or idea you aretalking about to something different.

Bob didn't finish his algebrahomework because his mind kept jumping the track to think about thenew girl in class.