He felt no pain, yet. He reached back to feel what he now believes to a be a nurse shark or a blacktip shark, judging from the gouges it left in his foot.
"He was probably four or five feet," Theobald said. "When I did that, he shook twice, then released and left."
An onlooker told First Coast News that she watched Theobald stumble and hop to dry land on one foot, screaming: "I got bit! I got bit! Get out!"
"He barely made it out of the water," another witness, Mike Webb, told the outlet. "He laid down at the lifeguard stand and they just went to wrapping and gauzing. His left foot was - from what he said was, he could see the bone on the top and the bottom."
Theobald said he may have tendon damage along with 10cm lacerations on both sides of his foot. And no sooner had an ambulance arrived at the beach to collect him than a second swimmer was attacked less than two miles down the coast, the City of Fernandina Beach wrote in a statement.
A 17-year-old boy was bitten no more than five minutes after Theobald, First Coast News reported. And though he, too, is expected to recover, the reports caused authorities to evacuate all swimmers out of the water along the beach.
Before that afternoon, only four shark attacks had been recorded in Nassau County in the last 135 years, according to the Florida Museum of Natural History, compared with more than 800 across the state.
The last encounter at Fernandina Beach took place three years ago, when a 12-year-old boy was dragged through waist-deep water by a shark nearly as large as himself. He had to punch the fish to break free.
Even though shark populations are declining due to overfishing, the museum warns that attacks can increase as more humans wade into their feeding grounds.
After the double attack at Fernandina Beach, officials flew red flags along the waterline to warn people away. Nevertheless, News 4 recorded a scattering of people wading late Friday afternoon even as a sheriff's truck rolled along the shoreline, urging them out with a loudspeaker.
"The shark has already bitten two people. Please exit the water," the driver said.
"There's a shark in the water that has already bitten two people," he repeated as he passed a small group waist-deep in the ocean. "I would move."