Mechanic
 

What is the proper mechanic for calling a runner out for being out of the base path to avoid a tag?

There's nothing listed in any of the "play pics" in the back of the manuals, as far as I know. So, just, point, call the out. Indicate the runner is wide by sweeping the hands to that side, if needed.

Usually just point and call them out. Everyone usually knows what you're calling.