I got busy and left my hammer hammer hanging where the sprinkler got it several time before I realized.

Now the handle is a slightly rough and I’d like to smooth it back up. I don’t want it to be slick but something that will protect the wood. I see mixed opinions on boiled linseed oil or a polyurethane spray. It’s not an expensive hammer, a decent Vaughn 23oz framer, but I like it.

To smooth it back up just sand it. I'd probably use 220 grit and sand until you get to the desired texture. A clear spray paint that's wood approved with seal it, keep in mind it will make it a little more slippery than what you sand the wood to. A flat clear, will probably be best to keep the slipperiness down.

Diluted linseed oil comes to mind. As light a finish as possible. Even better, scratch the back of your neck with the handle for an hour after a long sweaty day. Body oils will seal it up proper.