You know that you have to pick one and so you do. It doesn't matter that you can't tell them apart.
It doesn't matter that this is just a spar. That Naruto is suddenly so good at the shadow clone that even you can't tell the difference. Naruto is walking a wire, kunai sharp and wicked; the point at which his own talent and skills have far outstripped his actual experience. You can't tell him how to fix the problem because no one ever told you.
The clones are grinning and shouting insults, something that three years ago had been brash overconfidence but at this point is a legitimate tactic. You take out another three and fight the relief that trickles through the back of your mind when they fade to smoke. Naruto isn't the type to hold back and let his clones do the dirty work – he's always in the thick of things, fighting it out and never realizing he could die. The young never think they can die.
In your mind's eye you can see his face. A bloody grin crashing into the dirt.
You can't do this again.