Well, might as well quote the [CBS/Yougov][1] about this (March 13th):


> Even though a majority of Americans initially said they would back a no-fly zone, this majority vanishes once they consider that it could lead to a U.S.-Russia conflict. Support for a no-fly zone starts off lower than the sanctions to begin with, then drops off considerably when people are asked if it meant U.S. forces might have to engage Russian aircraft, and be considered an act of war by Russia.

"No fly zone" -> 59% for, 41% against.

rephrased as "No fly zone means act of war": -> 38% for, 62% against.


So, people are much more realistic once they understand the actual meaning better.  Past no fly zones were imposed on low-threat opponents (post Gulf War 1 Iraq, Serbia) so that might explain the relative initial enthusiasm: people probably figure it's a less risky alternative than "boots on the ground".

[Another/same Yougov poll][2], referring to yet other polls, exact question was "should the U.S. military should shoot down Russian military planes flying over Ukraine?"


  [1]: https://www.cbsnews.com/news/russia-ukraine-sanctions-gas-prices-opinion-poll-2022-03-13/
  [2]: https://today.yougov.com/topics/politics/articles-reports/2022/03/09/fewer-americans-support-no-fly-zones