Prosecuting, Melanie Ibbotson said police officers found Mr Shackleton, of Dovecote Drive in Ledston, Castleford, in the driving seat of a vehicle parked at the nature reserve.
The vehicle’s lights were switched on, but its engine was not running, she said.
Mr Shackleton’s solicitor Ben Whittingham said his client disputed being “in charge” of the vehicle.
Dressed in a suit, Mr Shackleton spoke only to confirm his name, date of birth and address.
He has made 12 appearances for the Blades since joining the club in July 2024. He came through the Leeds United academy.
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