Initial Play

Question
Good morning!  Could you please explain what "initial play" consists of? We were playing in a USSSA tournament this weekend.  R1 on 2 and R2 on 1, fly ball hit to left field.  R1 breaks for 3rd and F6 turns to go run out to left.  R1 stops and goes around F5, subsequently scoring.  F7 fields ball and throws it in.  Umpires confer and call R1 out, indicating that she had to allow F6 to attempt the initial play, even though the ball was in the air to the left fielder.  This didn't make a lot of sense to me, since by that logic F1 could start running to left field (same scenario) and R1 get called out even though F1 was not the one making the play.  (I hope this all makes sense!)  So I am trying to figure out when this "initial play" is no longer in effect.  Thank you for your help!

Answer
The initial play is the first play on the ball being attempted by a player that has a chance of making the play.

The description seems odd to me.  If F6 was playing in the normal position, she would have been behind the line that R1 would be taking on the way to third.  I am having a hard time understanding how there could be anything close to interference on this play.  Am I missing something?