At 76, Mr. Brown is seeking his second consecutive term as governor; the state’s term limits bar him from serving a third. (He was also governor during the late 1970s.)

If Mr. Kashkari needed another reminder of the challenge he faces, a Field Poll released Thursday morning showed Mr. Brown leading him by 16 points, 50 to 34. Perhaps even more troublesome for Mr. Kashkari, the poll found that nearly 60 percent of respondents did not know enough about him to offer a favorable or unfavorable opinion.

By any measure, the debate Thursday was spirited, and it often verged out of control as the two men talked over each other. Mr. Kashkari, in particular, spoke over the panelists, often pivoting off their questions to attack his opponent.

Mr. Kashkari said Mr. Brown’s response to a court order to reduce the state’s prison population — he ordered lower-risk offenders moved to county jails — was a failure and was leading to increased crime. When Mr. Brown said he would sign a bill just passed by the Legislature that would impose a statewide ban on single-use plastic bags, Mr. Kashkari said he would veto it if he were governor and cited it as an example of Sacramento wasting time while the state was in trouble.

Again and again, Mr. Kashkari criticized the ambitious high-speed rail project from San Francisco to Los Angeles that Mr. Brown has pushed even as it has lost popularity with voters and some lawmakers, and even as Republicans in Washington have said they would refuse to fund it. Mr. Kashkari said he would cancel the project if elected and cast it as Mr. Brown’s personal crusade.

“Make no mistake about it: He is raising your gas prices, you at home, he’s raising your gas prices to create the vanity project, what I call the crazy train,” he said.

In a moment that captured both his tactics and his choice of issue, Mr. Kashkari ignored a question about his political vulnerability and used his answer to attack the train project. “I think the question was, ‘Neel, how do you expect to win?’ ” Mr. Brown said when it was his turn to speak. “I’ll tell you, Neel, you don’t have much expectation to win, because things have been accomplished in Sacramento.”