This year marks the 50th anniversary of TENNIS Magazine's founding in 1965. To commemorate the occasion, we'll look back each Thursday at one of the 50 moments that have defined the last half-century in our sport.

No story in tennis has been as big, or as hard to fathom. Who would stab a tennis player? More than that, who would stab a 19-year-old girl in the back with a nine-inch knife while she was playing in front of a capacity audience?

That person was Gunter Parche, forever known in the tabloids as a “deranged Steffi Graf fan,” an overweight and disheveled man who wanted to help his favorite player overcome her younger rival and take back the No. 1 ranking. Mission—horribly—accomplished: His act of violence in Hamburg would force Seles to leave the tour for two years, and when she returned she would be a shadow of her formerly indomitable self. Graf would indeed regain No. 1 and win 11 more Grand Slams. As for Parche, he was deemed mentally unstable and never saw jail time. Because of that, Seles hasn't set foot in Germany since.

Maybe the worst thing about the whole sad story is that in April 1993, there really wasn’t much else that could stop Monica Seles. She had won seven of the previous nine majors and, after her title at the 1993 Australian Open, she looked like she might just tear through the season and win a calendar-year Grand Slam. Her father, Karolj, said that from a young age she had wanted nothing more than to hit a tennis ball. Seles at her early-’90s peak played in what can only be described as a trance. Nothing, it seemed, could wake her from it.

Before Seles arrived on tour in the late 1980s, as a 99-pound 15-year-old, it had been hard to imagine a fiercer fighter than Graf, but Monica matched her. There was nothing ladylike or elegant about her roundhouse swings—Seles slugged with two hands from both sides—or the pioneering grunt that she brought with them. In terms of both power and willpower, Seles upped the ante and pointed the way ahead. It’s no surprise that so many of today's players, including Serena Williams and Ana Ivanovic, cite her as an inspiration.

If there’s a moral or a lesson to Seles’ story, it may be that having the stuff to be a warrior in tennis, or any sport, is a more delicate proposition than we think. At first, Seles was tentative about walking back on a tennis court. By the time she became a fixture again on tour, she had lost the edge, the hunger, the youthful gusto—as well as the wiry physique—that had once made her unstoppable. If her stabbing shocked people around the world, imagine what it did to her, and imagine how hard that shock must have been to forget.

After the incident, Monica knew that there was more to life than smashing a tennis ball. She had been jolted, in the most frightening and permanent way, out of her trance. But in that brief, blazing, invincible period when she was in it, she changed the women’s game and set the bar higher for its future champions.