Step dancing history…it dates from the time when Ireland was continuously rebelling against rule of the British over them. With in turn the British trying to dominate the culture by stamping out all traditional aspects of Irish identity, including traditional Irish songs and dance. The Irish then had to started to their dancing behind the hedge rows, stable doors and behind the bar in pubs with their upper body straight and arms tight by their sides, so if spotted by English soldiers they wouldn’t be able to see them dance. Although a great story it seems a bit of a stretch to believe that a soldier wouldn’t know what you were up too with all the bouncing up and down in the same spot whither behind a bar or not.

https://ryanandodonnell.com/why-do-irish-dancers-keeptheir-arms-at-their-sides/