It's a broken or missing lever spring, they are held by a single screw through the bottom of the receiver in front of the lever pivot - if the screw is still there it's probably just broken.
https://www.gunpartscorp.com/products/1568780Chttps://www.gunpartscorp.com/products/1594660CI changed one in a Model 1897, It's been a long time since I did this but I think I found it impossible to get the spring flexed enough to start the screw with the lever in place so I removed the lever, started the screw leaving it loose, and then was able to get the lever back in.
Here's a picture showing the spring in an earlier solid frame gun where it's easier to see and in a later takedown.
