Sick yobs are tying razor sharp fishing lines between trees at neck height in woods popular with walkers, runners and cyclists - sparking fears that someone could be decapitated.
Visitors to the woodland off Birley Spa Lane in Hackenthorpe and Stone Lane in Woodhouse told how callous yobs have tied the thin wire in at least three locations in what could be a potentially deadly trick.
Resident Sean Harrison noticed them while walking through the woodland and was so angry he tore the wires down in disgust instead of taking any pictures of them.
He put an alert out from his Facebook page to other residents urging them to be careful when using the woodland, which has now been shared more than 500 times.
He posted: "People are putting fishing lines up in woods around Hackenthorpe and Woodhouse fields at neck height.
"Please be careful as I wouldn't like anyone to lose their head from some sick person putting fishing lines up. "
He added that a friend of his also noticed the wires while riding his bike and had to stop abruptly. The cyclist has reported the problem to Sheffield Council.
Mr Harrison said there are a lot of off-road bikers who use the woods and believes it is possible angry residents may have put the wire up to deter bikers from using it.
Other people commenting on his Facebook post agreed that it could have been placed there by residents fed-up with off-road bikers riding through the woods.
Ben Charles said: "It is because of people blasting about on bikes. It will take them straight off their bikes."
Natalie Farrell added that while she "doesn't agree for one minute" with putting fishing wire up, she added off-road riders are posing a "danger to kids and dog walkers."
This latest issue comes just weeks after Mr Harrison launched an online petition calling for the council and police to build a designated motorbike track to stop nuisance bikers running riot around the streets.
He said: "It's about time we made a stand to get a motorbike track for the city of Sheffield because if it doesn't get a track then it's only going to get worse.
"Sheffield Council and South Yorkshire Police it's time you worked with us bikers and not against us.
"Please sign this petition. Let's make our stand and no more riding on roads. Give us somewhere to go."
The petition has been signed by 350 people and it will be handed in to police and council chiefs if it reaches the target of 500.
One supporter, youth worker Lisa Williams, said: "I would love to see this happen. I would also love to see a project that promotes safety and motorcycle maintenance.
"Bikes and quad bikes are on the rise for young people and they need somewhere safe to enjoy riding them."
A Sheffield Council spokesperson said park rangers had checked the woodland but could not find any wires. They added that no formal complaint had been lodged either.
Sheffield District Commander Shaun Morley said: “Our officers will continue to seize and remove any illegal bikes that can be a nuisance and blight our communities, or worse a danger to responsible road users and pedestrians.
"The vast majority of motorcyclists in South Yorkshire are happy to comply with the law when out on their bikes and we welcome them.”