Will sophomores who didn't play much as freshmen be receptive to being redshirted?

What about even older players than sophomores?

they will hate it and take a work ethic hit. the longer they have been there, the bigger the hit will be.

I often redshirt sophomores if I am trying to balance out the class sizes. As long as they weren't promised a sophomore start, it won't be too bad. They will lose 15% of their work ethic, which isn't great, but isn't the end of the world either.

But if they were promised a sophomore start, then forget about it. They will lose about two-thirds of their work ethic.

And like papachooby mentioned, if you redshirt a junior or senior, they will hate it and their work ethic will plummet. They might even leave early.