Babe Ruth - Base on Balls

[Duke]

Just started working Babe Ruth this year after working softball for 10 years. Another coverted softball ump had to make this call and wanted to know my opinion.
Batter received ball four and runs down to first, overruns first base, turns into foul territory and returns to the bag. No attempt to go to second. Pitcher fires ball to first to tag the runner. Ump calls the runner safe and defensive coach explodes saying the runner is only protected to first base. In softball, runner is safe. Can a batter/runner overrun first on a base on balls in Babe Ruth. I cannot find this situation in the rule book.