By Ian Youngs
Music reporter, BBC News at Glastonbury
Winehouse appeared to lunge into the crowd near the end of her set
Amy Winehouse has returned to the stage at the Glastonbury Festival and appeared to throw a punch at a fan.
She lashed out at someone who tried to grab her hair as she finished her set alongside fans in front of the stage, her spokesman said.
She was followed by US rapper Jay-Z, who gave a triumphant performance to win over critics who claimed a hip-hop act should not headline the festival.
Other stars on a mostly sunny Saturday included Duffy and Massive Attack.
Winehouse's one-hour performance was her first full UK show for seven months.
It drew a huge crowd to the Pyramid Stage but split opinion among fans. Her spokesman said at least 75,000 people watched and that organisers had never seen the field so full.
"The 'lashing out' was when someone tried to grab her hair and she reacted," the spokesman said.
But footage of the incident did not clearly show what provoked her lunge.
The Grammy-winning singer was on fine form and in good voice for most of the set, going some way to dispelling fears about her health.
She jumped down into the security pit for the last two songs, separated from the fans by a crush barrier.
"Thanks for your support," she told them earlier, as she performed tracks such as Cupid, Rehab and Tears Dry on Their Own.
"I really enjoyed it - I've never seen her live before and I thought it was really good," said one fan, 18-year-old Lucinda Whitehead.
But Laura Bradley, 24, said: "It's a shame the crowd didn't appreciate her. They were slagging her off."
There appeared to be a smaller crowd for Jay-Z, but he was greeted by chants and cheers.
The New York hip-hop star fired up the crowd with an introduction that included a BBC interview in which Oasis star Noel Gallagher said hip-hop was "wrong" for Glastonbury.
Jay-Z then took the stage to the strains of the Oasis hit Wonderwall.
"So they say you guys didn't want me here to be here tonight," he said.
"They said you guys weren't into hip-hop." The crowd responded by chanting his name to show their support.
"Thanks for all the love here tonight," the star added, saying Glastonbury had "embraced my culture".
"This is a beautiful moment, I'm glad to share it with each and every one of you," he said.
The crowd went wild for the star's hits including 99 Problems, Hard Knock Life and Encore.
He seemed to succeed in winning over the many festival-goers who were unsure about his appearance.
Indie fan James Lucas, 26, wearing a Charlatans T-shirt, said: "It wasn't my bag – but yes, he was very, very good.
"When you see people at the top of their game, it's worth it."
Tom O'Shea, 27, from Neath, said it marked "a new era" for the festival.
"It breaks down boundaries and he was amazing in what he did," he said. "He's the best rapper in the world."
Jay-Z's set sampled songs by U2, Estelle, Rihanna, Amy Winehouse and the Jackson Five.
But one disappointment was the lack of any surprise guests.
His wife Beyonce, Coldplay star Chris Martin, NERD's Pharrell Williams, LinkinPark, Rihanna and Winehouse had all been rumoured to be joining him on stage.
Earlier acts on the main stage on Saturday included Crowded House, Manu Chao, The Raconteurs and Shakin' Stevens.
The sun shone for most of the day, drying out mud that was created by rain on Thursday and Friday.
Some 172,000 people were on site by Saturday morning, police said.
Crime has almost doubled compared with the same stage last year, with 342 reported offences, up from 177 in 2007. Much of that increase is down to a rise in thefts from tents.