A guy pulled this thing through the ice on my pond. Some sort of red ear?

Yep.

Vote for Pedro.

Hey Buddy long time hope you are well!

Yep that’s a RES with some nasty infection. They are susceptible to issues during our winters - I’ve lost caged RES over winter as well. Unless you experience this frequently I wouldn’t worry too much about it - I figure I lose a percentage of RES every winter due to our temps.

Funny how slightly different fish sometimes have widely different responses to environmental stressors. In 2017, a sudden fall cold snap devastated my plus 6 inches CNBG population with a white fungus. RES were totally fine, as were small CNBG.