From humble beginnings … parents may now need to hire secuirty guards to keep backyard parties under control.THEY seemingly did everything they could. Harry Staples’s parents hired security guards, had an invite-only list, planned a midnight shutdown and notified police about their son’s 18th birthday party in Forestville earlier this month.

But the party took a dark turn just after 11.30pm when two people, who were earlier ejected, returned with others and allegedly started pelting building materials at the crowd, leaving Liam Knight on life support after a metal pole pierced his head.

The attack has left many parents petrified of hosting house parties and highlighted how quickly and easily such events can get out of control.

The humble backyard party has become such a minefield that experts say parents would be mad not to have professional security, RSA marshals, bag checks, floodlights, wristbands, metal detectors, an alcohol plan, a thorough casing of their house prior and police notified.

”There’s a whole change in attitude with Gen Y,” said former police officer Mark Ellis, who runs a party planning and security business, Gatecrash Security.

”They have little respect for authority – whether it’s parents, police or security – and certainly for people’s property.”

He said the number of teenage parties he supervised had doubled each year since he entered the industry and they all attracted uninvited guests. About 10 per cent ended with serious gatecrashing incidents.

”The problem is mobile phones,” Mr Ellis said. ”If people come to a party and there’s no security and bad fencing, they’ll text five mates in the first five minutes and then it starts to multiply.”

At least six parties have spiralled dangerously out of control in the past six weeks in Sydney.

On the same night 17-year-old Liam was speared in the head, Sanjay Mahendran was glassed in the face when he told a group of gatecrashers they could not enter his 18th at a Seven Hills community hall.

A mix of boredom, braggadocio and peer pressure leads young people to gatecrash, experts say. ”It’s a feather in their cap,” said a former policewoman, Naomi Oakley, who runs the Safe Partying website.

One teenager, who did not want to be named, said parties often felt like the only entertainment option when underage.

”Often you don’t go with the intention to jump but if you can and others are, you will,” he said.

He attended a party at East Lindfield, which was similar to the one at the Staples’s home. When gatecrashers were refused entry, they went next door and pelted beer bottles at the crowd.

”People were dropping like flies,” the teenager said.

He recently snuck into a party in Northbridge through a hole in a side fence, yet an hour later ”most of the fence palings had been kicked off and a herd of people were trudging through”.

”I saw people stealing knives, bowls, TV remotes, anything,” he said. ”At one point the mum was running around trying to kick people out. There was one security guard but he was overwhelmed.”

Ms Oakley, who has supervised 500 parties without incident, said a trouble-free night required planning and professional help.

”I can’t stress enough that 95 per cent of the party will be reliant on how you serve or manage the alcohol,” she said.

She bags, labels and serves all alcohol and monitors anyone getting too drunk.

The NSW police said gatecrashing incidents were not increasing but the consequences were becoming more concerning.

The original release of this article first appeared on the website of Hangzhou Night Net.