How would you address this with your partner?

[jkumpire]

"Hey (PU), why did you eject #12?"

Then it becomes a conversation based on his answer. Let's say the originator is right and he did eject him for MC.

"You know, (PU), the MC call is mine to make, why did you poach it?"

On the field, you can't overrule your partner on something like this. Nor can you eject someone when he is standing in front of your partner on a play that's not yours.

But after the game, you take care of the problem.