Mystery surrounds a "senseless" attack on a village sports pitch owned by the King.
Grass has been killed on one of the playing surfaces at Dersingham Rovers FC's ground off Manor Road in the village.
The field is leased from the Royal Estate by Dersingham Parish Council and has been used by village football teams since the early 1900s.
It is not known whether King Charles, who is recuperating at nearby Sandringham House after undergoing cancer treatment, is aware of the damage. Police are investigating.
Zig-zag marks suggest weed killer was poured by someone walking across almost the length of the pitch, while a large area of grass has also turned brown.
Buckingham Palace referred enquiries to Dersingham Parish Council.
Its chair Coral Shepherd said: "It's stupid, senseless, mindless - so many people get so much enjoyment out of the sports ground.
"I fail to see what they feel they'll achieve by doing it, it's a pointless exercise."
Borough councillor Judith Collingham, who chairs the village tennis club which also uses part of the sports ground, said: "People are very upset, it's so completely ridiculous - why would anyone want to do this?"
Rovers under-15s coach Paul Lough tweeted: "Yet again more vandalism at Dersingham FC.
"This time weed killer on our main pitch. More hours that volunteers have to spend to repair the damage caused by pathetic idiots with nothing better to do than try and stop youth and adult teams playing football."
Last summer a window was smashed in a shelter and advertising hoardings were torn down at the ground, where 13 youth teams pay. Five years earlier, a building was set alight on the ground.
A Norfolk police spokesman said: "We are investigating a report of vandalism on Manor Road in Dersingham. It’s believed to have happened between February 7 - 10. If anyone has any information please contact us quoting crime ref 36/10339/24 via email: SNTDersinghamandGayton@Norfolk.police.uk or by phoning 101.
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