Start of a new inning

[Jtaylor33]

so a fellow umpire in a chain email is asking about start of a new inning.

During rec ball season

Games are 90 minutes, with no new inning to start after 80 minutes.

Inning ended at 79 minutes and evidently a coach raised hell over the teams not getting their full time. ( other issues in this as well, game was uncatchable, 4 run max per have and team was down 6.)

I guess one of the umps ended the game, do to the fact that the girls couldnt get on field and warmed up before the 80 min. I chimed in that the inning starts as soon as the previous inning ends.

Can someone help with when the inning actually starts and where in the book it states this? Or am I wrong?