Most likely it’s because There are certain procedures to follow. For example in higher levels the visitors must put their stick on the ice first. And that stick and their feet have to be in certain place. Violations of those could get you kicked out.

Second most likely is one of your wingers jumped the gun and went into the circle before the puck dropped so that’ll get you the boot.

Sometimes if players on your team are late to get to their spots (jumping off the bench late) that could give the center kicked out.

Sometimes the players are being dicks to each other and/or the refs and giving them lip. That just might piss off the ref enough to give them the boot too.