Both of them backed off their verbals, and eventual Indiana pledge Romeo Langford cut Louisville from his list of schools. (source)
The meaning is clear, but I find the usage of "back off" as a transitive phrasal verb strange. I am more familiar with "back off on" and "back off from". For example, Merriam Webster has a sentence that employs the same meaning of "back off":
you'd better not back off on your promise to do all the planning for the big dance
Is this omission of preposition in the quoted sentence idiomatic? Also, do "back off on" and "back off from" have the same meaning?