What model Western?
I'm not an expert, but I don't remember them making a knife with cracked ice or other synthetic handles.
They only used natural materials as far as I know. (ok, the "F" series "Black Beauty" knives had stacked aluminum and fiber washers) but the rest were wood, leather, or stag.
Maybe a previous owner rehandled it?
At any rate, is the play more rotational or fore/aft?
Is the guard tight against the handle or is there a slight gap?
My first thought is to use some epoxy to secure the guard to the tang and handle.
I would not hit it with a hammer.