What is the etymology of the term 'hunch'?

Oxford states the etymology as:

late 15th century: of unknown origin. The original meaning was ‘push, shove’ (noun and verb), a sense retained now in Scots as a noun, and in US dialect as a verb. [The] noun derives probably from a US sense of the verb ‘nudge someone in order to draw attention to something’.

Hunch in Scots means ‘push’ as a noun. Did the Scots not use it as a verb? Why did the US use it as a verb?

In the example below, the meaning of ‘hunched over’ is ‘bent over’ according to the Guided Compositions book.

The usual hectic traffic awaited me as I hunched over the steering wheel of the company car.