On a spring day in recent memory, I was strolling up Ninth Avenue alone, after leaving a bistro lunch with a gentleman caller and my soon-to-finish-N.Y.U. son. It was sunny but not yet steaming. Businessmen had their ties tugged loose or suit jackets slung over their shoulders. There were floral frocks and filmy blouses among the adorably pierced and punked-out goths of Hell’s Kitchen. I could almost feel the financial yoke of my son’s college tuition slipping off my neck.

Then an approaching guy chatting equably with a tall friend dodged at me to grab my crotch. I don’t mean brushed by it maybe accidentally; I mean he grabbed between my legs with a meaty claw, big as a waffle iron. He also called me the C-word with breath that stank of beer. Then he passed on into a sandwich shop with his buddy.

He wore a royal-blue plaid short-sleeve shirt you might find in a J. Crew ad, nicely hemmed jean shorts, and pricey sneakers. He was half my age and twice my weight and had the wide, muscled form cultivated by Equinox aficionados. Translation: he wasn’t dope sick or a flat-out loon.

In case you haven’t been on the receiving end of this sort of assault, you should know the primal physiological response it evokes—in this woman, anyway. The stomach drops, as if you’ve been shoved backward from a skyscraper and are flailing through space. Time dismantles. There are more frames per second, and people’s facial features become very specific. This guy had a squashed-down forehead, wide-set eyes, and heavy but neatly waxed brows.

Cops later told me my description was uncannily detailed—the result, I think, of the kind of change in perception post-traumatic-stress experts call “hypervigilance.” The reptilian area of the brain jolts you either to do battle or to bolt. Adrenaline and cortisol juice through you like a hit of meth, so you might find yourself still up and jittery at 4 A.M. (maybe even watching something as god-awful as “Waterworld,” the way I later did).

I stood outside the doorway of the sandwich shop—pulse pounding in my ears, my heart doing mule kicks in my chest. Inside, the Grabber, as I thought of him, was waiting in line to order a sandwich. He was fine; I was the one with the problem.

Shame hit, a cold backwash of elemental shame: something bad had been done to me; therefore I was bad. Even though I knew better, I started scanning for how I’d incited this. Pedestrians glided past. A sandwich was being made. I took stock of what I had on: in some ways, I wish I had been wearing booty shorts and Lucite heels and prissing past the Port Authority Bus Terminal holding my décolletage in my hands and saying “hubba hubba.” I should be able to dress that way if the urge possesses me.

Instead, I was wearing a modest dress and platform slides with big cork soles to save the feet from pounding concrete. For an instant, the shoes looked radiantly slutty, the old-maid equivalent of dominatrix spikes. I was drenched in sweat, and part of me wanted to bolt the two blocks to my apartment, scramble up the stairs, double-latch the door, and crawl behind some heavy furniture. But inside all that noise in my head, some space bar got hit, and a moment of quiet opened up.

One good side effect of a childhood as chaotic as my own is that I’ve worked up habits that can pay off in the middle of a butt-whipping. (I take twenty minutes of silence morning and night, and I see a therapist.) While the Grabber paid for his tidily wrapped sandwich, I noticed all the young women passing by—some, yes, in booty shorts, and with bodacious tatas—and I thought, If this sick bastard will do this to me in broad daylight, what’s he doing to these young’uns at 3 A.M.? My mind shuffled through the myriad times that run-ins like this had happened before. Then I came to and shouted from the doorway, “Not today! Not this bitch! You picked the wrong woman to fuck with today!”

The counter guy, bills in hand, craned around the line to see the madwoman outside. As the Grabber half-turned, the size of him shocked me and I backed away farther, to the other side of a parking meter, where my eyes could still shoot flying cartoon daggers at his broad back, albeit with some yardage between us.

Then a voice rose from the sidewalk. “What’d he do?” It was a man on a rectangle of cardboard you might normally step around.

“He grabbed”—polite words didn’t seem fierce enough, and the gross ones struck me as obscene—“my private zone!” This was the name my kid’s grade-school teacher had used for any area covered by a bathing suit: private zone.

So many guys might shrug it off: What’s the big deal? This one jutted his jaw out, saying, “He cain’t do that” with such fire that I started dialing 911. In a moment, I was on with a police dispatcher, describing the Grabber as he got his change and hustled out of the shop with his friend. They ignored me and started to get away, walking fast toward the bus station. My new friend on the cardboard said, “Go, go, go!” and I started to trot. They broke into a sprint, outpacing me right off.

Around Forty-first Street, a cop car pulled up, and I hopped in and recounted it all as they peeled out like they do on “Law & Order.” The female officer riding shotgun radioed the description I gave her to other cops, who nabbed him and hauled him, handcuffed, before me outside the Port Authority. “That’s him!” I said. He was blank-eyed, as if this whole thing were happening to somebody else. His buddy was amped up, though, claiming his friend hadn’t done anything. I shot back that that was horse hockey—yes, he had—and the buddy walked off as an officer put the Grabber in the back of a cruiser.

How satisfying was all this? Very.

En route to the station, the female officer looked back through the cage: Did I need counselling? I told her I’d had enough counselling to chase the sucker up Ninth Avenue. I only wanted to press charges.

I filed a report. Later they told me the guy was a thirty-something from Jersey. He had a light rap sheet with no record of sexual assault. Nobody ever called me to court, but the cops had cuffed him, dragged him out of the bus station, and booked him. A woman should be able to count on follow-through from the justice system—they’d eventually fail to charge him—but at least he spent a night at Rikers. At the time, I felt somewhat vindicated.

For days after, I kept chewing on what thrill the Grabber got from his move. It just won’t translate to my gender. There are plenty of guys I might fancy kissing on the mouth, but to grab a passing one in the crotch and say, nice package? One pal joked, “Oh, yeah, try it,” suggesting that, for men, any sexual overture is welcome. I asked how he’d feel if a fellow weighing three-forty cornered him somewhere isolated and manhandled him. Suddenly this struck him as way more sinister.