06/29/2008 at 09:00 AM EDT
is back on stage – and she's in fighting form.
At the end of her hour-long performance Saturday before nearly 80,000 festivalgoers at the Glastonbury Festival in Somerset, England, the singer climbed down from the Pyramid stage and threw a punch at a fan, the Associated Press reports.
Witnesses say that a fan tried to grab the singer, though it is unclear what provoked the altercation.
Despite the scuffle, Winehouse was reportedly in fine voice, peppering her set with songs from her Grammy-winning album Back to Black,
including "You Know I'm No Good." Before she sang "Wake Up Alone," she told the crowd, "I wrote this one for [incarcerated husband] Blake [Fielder-Civil.] I thought I'd never see him again."
The beleaguered Brit, 24, then mumbled a bit, and told the crowd: "I've only got two weeks left of this predicament, so this one's for you, Blake."
Following her performance, Winehouse changed into more casual clothes – a striped T-shirt and shorts – before scouting out a headlining set by rapper Jay-Z, which she watched next to his wife, Beyoncé
Earlier in the weekend, Winehouse surprised fans with a two-song performance
as part of Nelson Mandela's 90th birthday tribute in London's Hyde Park.
The singer looked healthy, according to reports, and gave her husband some attention with a heart-shaped adornment that featured his name, which she wore in her hair.