It means Going Aggro in a battle. As for examples, take any example that would be covered by Going Aggro, and have it happen during a battle, like so:
A battle is raging, gunfire everywhere. Ampersand the Gunlugger sees Rolfball, the treacherous rat, running across the battlefield -- he's trying to get to a jeep somebody abandoned during the fighting! Ampersand's player is like "fuck no, Rolfball, you are not getting away that easy -- I fire a warning shot from my AK right in front of his nose and shout out 'Get the fuck back inside, Rolfball -- I'll deal with you later!'"
or another battle is raging, explosions and bullets flying everywhere. Klaxon bursts in through the doors of the previously secure bunker where the enemy hardholder's mostly-not-that-armed civilians are cowering. Though some of the civvies are armed they clearly weren't expecting this, and they definitely aren't going to fight back, at least not right in the moment. Brandishing her flamethrower she shouts 'put your hands where I can fuckin' see 'em!'
I mean, anything can happen as part of a battle, generally speaking, and so NTBFW means that if the PC ends up Going Aggro in such a context, they're gonna do extra harm at the very least. Arguably, as in the second example, you might decide that NTBFW allows them to Go Aggro on a larger group of people than might otherwise be reasonable.