Eleven-year-old Harper Gruzins practiced "The Star-Spangled Banner" for weeks, but spectators showed little appreciation when she performed it Saturday at a Major League Soccer game in Dallas.

About 22,000 fans inside the stadium offered some polite applause, and a few boos, but the reaction online has been swift and harsh.

The blog Deadspin called it "the worst national anthem rendition ever," and people on Twitter weren't any kinder. Some Tweets characterized her performance as "tragic," while another said it was worse than that of Roseanne Barr's, who sang the anthem off-key at a baseball game in 1990, then grabbed her crotch and spat.

Viewers of a video of Harper's performance will notice that she appeared to slow the tempo of the song, injected many vocal flourishes and had less-than-perfect pitch.

She acknowledges that it "wasn't my best performance," but told ABC News' Ryan Owens in an interview that the sound of some fans' horns threw her off-key.

"I started to sing and was like, 'That's the wrong key.' Once you start the national anthem, you don't want to start over and humiliate yourself," she said.

Her parents rushed to her defense.

"Things people are saying are really heartbreaking. And just mean. Spiteful and mean," her mother, Kelli Gruzins, said.

Her father, Karlis Gruzins, said the reaction has been hard to handle.

"What I feel like doing is just unplug her, take her out of everything and just protect her. Hide her. Keep her from people hurting her," he said.

Other far more famous singers have also taken heat for botching the national anthem, which is famously hard to sing.

In January, Aerosmith's Steven Tyler endured countless jabs after screaming the song before an NFL game.

In July, country music singer Luke Bryan apologized for reading the words to the anthem off his hand while singing at the Major League Baseball All-Star game.

Christina Aguilera flubbed her rendition of the anthem at the Super Bowl earlier this year. She hit all the right notes, but mangled the lyrics.

In 2009, pop singer Jesse McCartney skipped multiple verses of the anthem while performing at a NASCAR event in California.

Like Bryan, singer Michael Bolton broke from his overly passionate performance of the anthem to look at crib notes scrawled on his hand at Boston's Fenway Park in 2003.

And singer Macy Gray was booed and ridiculed for her tentative, offbeat rendition of the national anthem at the Pro Football Hall of Fame exhibition game in 2001.