"It's not my call" (politely)

[JC]

I generally say something similar to rainmaker's suggestion.
"My partner had a very good look at it"

I also add this sparingly. If I am near the coach when the play happens across the court and the coach asks me about it, I say
"Coach my partner had a very good look. I have no idea, I had the same view you had."
It's usually 2 possessions later before the light goes on.
Again, use SPARINGLY.