I hate ads that automatically play. One of the worst was on the NFL.com fantasy site. It was a Geico advertisement. The loud audio starts with no action on the viewer's part and it says something like "You can't stop this Geico ad from playing because it is already over!"
Anyway, all auto-play audio and video ads are disabled here. As a side note, I have all nuisance ads disabled, such as pop-overs, pop-unders, interstitial ads that force you to click so that you can read the next page, etc.
There are multimedia ads, but theoretically you have to mouse over it for a few seconds or click it to play.
Of course, some advertisers break the rules, but with enough information I can put in a ban request.
I do note that sometimes if you are on a desktop, the mouseover range can be a little generous, and I've seen it sometimes to where if you move a mouse over an advert and then off the window if the ad is at the edge, it will start the playback.
If you see it again, can you please verify that it plays automatically without any chance of the mouse being near or over the ad? And note which ad location, for example, I think you mean the left-hand large rectangular ad at the top, next to the Clek/Nuna ads? Nationwide.com might be enough to ban it, but if you are willing to see the destination URL, that would be more information I can use.
I am watching for a Nationwide as here also, but many ads are targeted based on your region or browsing history so it may not appear for me. I have not seen an autoplay ad here that I was able to confirm in a long time, but ads vary so much that even though I have a lot of page views, I probably don't even see 10% of what other members see due to targeting.