Oh, he knew. He planned it all! For WEEKS, he KNEW he could get Grace to hit herself with a volleyball if he only chose his moment!

Or, more likely, he did not.

Confession: While it was in-character for Justin to caution Grace about showing off her super cool strength (he is a genre savvy super hero fan, after all), the actual reason I wrote him doing so was so he'd be in place for this comic.

And yes, Justin has pre-existing awareness of the (literally) huge nerd.

He might be a fan. I'm not sure.