The chances of being banned are not related to whether you post solely on one board or not, but rather to weather you break any of the rules that lead to being banned, which can happen regardless which post you post in.

Writing on boards you are not skilled with does not warrant a ban, lest the content being posted be complete utter and reiterative nonsense (and even then, it will probably only lead to such post being deleted if reported for adequate reasons).

Most common bans are due to posting copy/[spin]/paste content without citing the source. It’s pretty basic not to incur in this practice, and it seems rather unnatural, likely derived from people’s will to try to make-up for their lack of knowledge by resorting to this practice, chase merits, comply with some campaign quota, or pretend to know something they don’t.