Interesting play............

[NM FP Ump]

Cajun,

I think you got it right. Even though the result of the interference by R1 could have aided the defense to get an out, you have to call dead ball immediately and return the runners to the base(s) last touched at the time of the interference. If you didn't kill the play and there was an out at home on R2, the OC could say that the defense was aided by R1. On the other side of the coin, if R1 accidentally kicked the ball into the dugout, she would have aided the offense (2 base award from the throw) and the DC would be yelling. The rule is worded so that neither team gets an advantage.

Had a similar play this weekend. Same rule set, 12U (thought you were my partner for a moment). Batter hits ball to F5, F5 underthrows the ball to F3, BR reaches 1st base and the ball caroms off the dugout pole, back to the BR, who then kicks the ball into RF (inadvertent kick). I killed the play right there. No other runners on, but the BR wanted to take extra bases.