Redhawk Caldera Mama said knock you out

Just as she would do with Wildfire in a few short days, Fox intended to be the victor for this spar. Each and every one of her pups would have to know what it was like to lose, and she would rather that they experienced it at her tooth and claw than an enemies (at least the first time around). Losing wasn't fun—it could be downright terrifying—but it happened to everybody. Yes, even the greatest warriors: Fox and Peregrine. The more fights one lost, the more they could learn from their mistakes. Eventually, losing became less and less frequent (as was the case for Fox), and besting opponents got easier.

So when Nightjar demanded that his mother "show him," how it was done, Fox took it to mean "show me how it feels to be on the losing side." She wasn't rough with him, of course, but she rushed him with little time to maneuver out of the way, intending to pin him down. Perhaps he would learn at least a little something from it (namely: never give your attackers the first move).