UNO's-One Word Tempo Play Calls 

As long as the officials have marked the ball ready for play you are fine. If you are under these substitution rules then the officials will come in and pause the "tempo" in order to allow the defense to substitute. But if the ball is marked ready for play and there is not an official over the ball play as fast as you want.

My guess is this. I think when a new player runs in, he has to go past the numbers. This is to avoid those sleeper plays where a player takes one step off the sideline just before the snap and they throw him the ball.

if you run a tempo offense and your sub players on and off the field you have to give the defense an opportunity to sub a player That is the rule they warned you about if a defensive player is trying to sub you have to wait for them. I got warned in high school and a smart coach would tell his DL to walk off the field to give the defense time to set up if the offense does not sub that is no longer a rule.

Coach are you still active on Twitter? Couldn’t find you on there. Would love to discuss some terminology with you on this. Thanks!

Coach wouldn’t the other team eventually figure out the play if you called bronco , etc throughout the game? Thank you sir.

It is illegal, no matter what level you play at, if you substitute on offense the defense has to be allowed to substitute. If you don't substitute on offense and the defense tries to substitute you don't have to wait.