One of the headliners of a major Hatfield music festival has dropped out.

Sum 41 will no longer play Slam Dunk Festival South 2021 in Hatfield Park next month.

The Canadian Fat Lip and In Too Deep band were due to co-headline the twin-sited festival with Don Broco.

Four Year Strong, Me First & The Gimme Gimmes, The Vandals, With Confidence, Crown The Empire, Ice Nine Kills and Free Throw will also no longer appear as SDF.

Bedford's Don Broco will still headline the Rock Scene Stage in Hatfield and Leeds, according to the latest line-up poster released by Slam Dunk organisers.

NOFX, Frank Turner & The Sleeping Soul, Alkaline Trio and Pennywise are on the Punk in Drublic Stage.

The Jägermeister tent will feature two stages with no clashes with While She Sleeps, Bury Tomorrow and Funeral for a Friend all on the bill.

The pop-punk, ska punk, metal and alternative rock festival is due to return to the grounds of Hatfield House in Hertfordshire on Sunday, September 5.

Due to the pandemic, the Hatfield festival has already been rearranged three times, with multiple line-up changes since the first acts for Slam Dunk 2020 were announced back in 2019.

With a number of international artists pulling out due to travel restrictions, a host of British bands have been added to the bill, including Creeper on the Rock Scene Stage.

With the festival's future in doubt, Slam Dunk posted on its social media channels a statement explaining the line-up changes.

Slam Dunk's update read: "Last week was a turning point for the festival. With just one month now to go, international artists had to make final decisions on whether they could make the trip to the UK or not.

"They need to start booking flights and paying out other non-refundable expenses. Truth be told, it did at one point look like we would lose all our international artists.

"But then a miracle happened and the UK opened up quarantine free travel to double-vaccinated US and European citizens.

"Unfortunately for some, the change came too late and coupled with other restrictions, meant they can no longer come.

"So it is with regret that we have to inform you these artists won’t be playing SDF21: Sum 41, Four Year Strong, Me First & The Gimme Gimmes, The Vandals, With Confidence, Crown The Empire, Ice Nine Kills & Free Throw.

"However we are pleased to welcome these UK artists to the bill… Creeper, Brutality Will Prevail, NoahFinnce, & For You The Moon."

Organisers are offering ticket holders a refund for those that no longer wish to attend.

Team Slam Dunk added: "However we are pleading with you, the fans, to still attend SDF21 and support us and all the artists still playing.

"We truly depend on it. For those of you that still attend, you will receive a discount and early access to tickets for SDF22.

"To those who ask ‘why not just cancel’ the simple answer is that if we do not attempt to do the festival this year, there might not be a next year.

"Many people don’t realise we are a small, independent company that revolves around, and relies upon, putting this festival on.

"Hundreds of other people, from staging, sound and light companies, food vendors, security, and the bands still ready and willing to play, are dependent on us to offer them a chance to work after 16 months of our industry being left for dead.

"Your support directly contributes to so many people staying in a job. The artists booked to play this year will not roll back another year, most already have their own tours and plans booked for 2022.

"Many will ask, ‘why don’t you replace artists with some big-name UK artists’ believe us we have already tried this at every available opportunity.

"Although you may look at a band’s schedule and see they are free over SDF weekend, there are many reasons behind the scenes that could prevent an artist from playing.

"We know that for many of you, this is not the same line-up as when you purchased your tickets. For some of you that is as far back as September 2019 – and the festival has been through three reschedules and various line-up changes since then.

"We could not be more appreciative of those of you who have stuck with us through thick and thin.

"That being said, we fully understand the disappointment from others after so many changes.

"Throughout this unprecedented and scary time in our industry, we were determined not to lose faith and deliver you all an event filled with the joy and revelry that only live music can bring.

"We are still determined to do that. It may not be what we had originally planned, but it will still be Slam Dunk Festival."

The statement concluded: "For SDF21 to work we need our community to come together now - and we can only do this with your support.

"Hold onto your tickets, keep your travel plans in place, get your COVID tests or vaccinations sorted and defy the odds by making this happen.

"We want to say a massive, heartfelt thank you to everyone who has stuck with us and we can't wait to see you at Leeds or Hatfield in just a few weeks.

"We are so close now, we will not give up… we all need and deserve this event."