The Bexar County constable was called out to Mission San Jose after receiving a report that a man was stirring up trouble.
The incident happened at around 11 a.m. Wednesday.
Texas Parks and Wildlife officials said a man was bothering several tourists.
Witnesses said the suspect was belligerent.
Officers were forced to use a stun gun on the man. They say they aren't sure what set the man off.
He was arrested and is undergoing a medical evaluation.