I work NFHS softball. Our rules and case book have no guidance on how to judge when a "tag attempt" has begun, and thus when the basepath is established. I don't know if NCAA has any guidance. But I did find that MLB does provide this guidance in the minor league manual:
“When determining whether a base runner should be called out under Rule 5.09(b) (1), so long as the umpire determines that a play is being made on the runner and an attempt to tag is occurring (i.e., the fielder is moving to tag the runner), no physical tag attempt is required to call a runner out for leaving the basepath."
So, that is the guidance I use. I have been in some heated discussions in other forums about this. Many umps believe that there DOES need to be a physical tag attempt, or that the fielder needs to be within tagging distance. I don't believe either of these two things be true in order to judge it a tag attempt. I think if the fielder has the ball and is moving toward the runner in a clear attempt to tag them out, a "play is being made on the runner" and thus the basepath is now established. They don't need to physically reach out.
How do you judge a tag attempt?