Batter-Runner Unintentionally Kicks Ball

 
With no outs and runners on first and second base, the batter (B1) chops the ball down the first base line. While running to first base, B1 unintentionally kicks the ball. The first baseman is still able to field the ball and tags B1 well before he reaches first base. The runners advanced to second and third base on this play.
 
The umpires were offered these rule interpretations from the helpful offensive and helpful defensive coaches:
 
A) B1's contact with the batted ball was unintentional and resulted in B1 being tagged out, so "play on"
B) B1 had not yet reached the 45-foot runner's lane, so he is not at risk of being called out if he is hit by a batted ball, so "play on"
C) B1 is out and the runners are returned to first and second base.
D) B1 is out, but the runners can remain on second and third base.
 
What do the umpire do?
 
Call
When the batter-runner is struck by a fair batted ball outside the batter's box, the batter-runner is immediately out, the ball is immediately dead, and runners may not advance. In the play below, B1 is out and the runners must return to their base at the time of the pitch. B1's position relative to the runner's lane and B1's intentions are not a factor -- answer "C" below.