It is a random-post widget script. When checked with speed tool, the javascript: https://mysite.blogspot.com/feeds/posts/default?alt=json-in-script&callback=rp_results_label&max-results=10 was remarked as a render blocking JS. I tried adding either both "asyn" and "defer" in the script. And the widget disappeared. How do I fix this?
Being that it's blogspot, that's out of your control. NOT something you get to change. I'm a bit surprised you'd even be able to add attributes to it since ... are you sure you're using blogspot? Basically, you're SOL. S*** outta luck if so. Hence @sarahk's comment. Though, without seeing the actual site and knowing what the offending script does, even if you could change it we can't tell you how or where. "random post widget script" could mean almost anything, though it sounds like a crappy poorly written third party extension / mod / plugin / pickAHuffingNameForTheseAlready, That said, generally the first move to fix this is to move it out of <head> and to right before </body>. But that only works if the script is applying itself to the existing markup properly, something I can't guarantee without seeing the offending script and the markup it is being applied to.
The attributes async and defer can only be used if the script is placed in the head section of the web page. If the script is placed in the body, the async and defer attributes aren't recognized. Other than that, I don't know enough about what you're working on to give any answer.