“He’s a Rugby League Superman!” a television announcer shouted during a Hayne burst.

“Superstar, superhuman,” went another call as Hayne sprinted through and around opponents. “Call him what you like. The speed of a bullet!”

Last October, in a letter to the “Blue and Gold Army,” the fan base of the Parramatta Eels, he announced his intention of playing in the N.F.L. He was in line to become the highest-paid National Rugby League player, likely to earn more than $1 million a year, but gambled on a sport he had never played.

“It’s always been a dream of mine to play in the N.F.L., and at my age, this is my one and only chance at having a crack at playing there,” he wrote.

He ran a 4.53 40-yard dash for N.F.L. scouts in December and signed with the 49ers in March. He has a three-year contract reportedly worth about $1.5 million, with only about $100,000 of it guaranteed if he does not make the final roster.

His odds appeared to be unlikely at best a week ago. Now, he has the Bay Area and a continent across the ocean cheering him on. San Francisco coaches have done their best to play down expectations — “It’s the first preseason game — it’s not like we’re playing Week 8,” the special teams coach Thomas McGaughey said — but find Hayne a scintillating talent.

“He can play in space,” Coach Jim Tomsula said after Saturday’s game, presumably meaning in the open field, not the outer atmosphere. “He’s a premier athlete in the world in space.”

McGaughey called Hayne “fearless” and said he had “great lateral quickness.” Both characteristics, he said, are found in the best returners and runners.