SUSHI AT THE BALLPARK
By Bob Timmermann
Discounting the obvious answer that at Japanese parks, you've likely been able to buy sushi for quite a while, the first reference I could find to a California stadium selling sushi was in 1989 in San Diego.
It was introduced on Opening Day in 1989 at (then) Jack Murphy Stadium.
Its introduction was not met with overwhelming approval by the locals.
This appeared in the LA Times of April 4, 1989 "This sushi stuff is ridiculous," said San Diego Police Officer Rick Schnell. "They ought to be selling hot dogs and hamburgers. They've never done those that good to begin with. Sushi makes us the wimp capital of baseball--at least until October, when we'll beat everybody. But in October, when the World Series comes here, selling sushi will be embarrassing. We'll have to be extra good just to cover up the scorn."
An article later in the year in the same paper mentioned that the Angels were going to start selling sushi in 1990.
I'm not certain about the Bay Area teams, but I was in grad school at UC Berkeley in 1987 and 1988 and I spent quite a bit of time at the Oakland Coliseum and there was no sushi for sale there. I cannot speak for Candlestick, but I would have my doubts about that park selling sushi at that time.
The Dodgers started selling sushi some time in the 1990s, but only in its cafeteria on the club level. In 1995 when Hideo Nomo joined the team, there were roving vendors of sushi.