run downs

Question
Can you describe some of the rules regarding what would be obstruction regarding a rundown?  For example if a runner is stuck between 2nd and 3rd and the third baseman "shortens the gap" to receive the throw and the the runner makes contact with the third basemen while the ball is in the air.   Does that constitute obstruction?   If you need more information please let me know.

Answer
Hi Zach,

A rundown improperly run is a very good way for a runner to get out of a pickle.  In my experience many teams run bp but very few practice this, I guess relying on what they remember from hs.  It is not unusual at all for the runner to get an obstruction call on a rundown, I've seen and called it many times.

Ok... obstruction is the act of a defensive player not in possession of the ball (or in the act of fielding a batted ball) that hinders a runner legally running the bases.  

In your q F5 does not have the ball (about to receive doesn't count) and is in the path the runner is taking to 3rd when contact is made.  We have a DDB, Obstruction, and when play is over we call time, and then we award the runner the base they would have made had they not been obstructed.  In ASA it may be 3rd in this instance or we may send them back to 2nd (would HTBT).  

Mark