Showtime officially announced production on an unscripted series featuring the World Series champion San Francisco Giants during David Nevins’ first appearance before the Television Critics Assn. as the pay cabler’s entertainment prexy.

The untitled series will aim to capture some of the audience of HBO’s football-focused “Hard Knocks” skein but will differ by following the Giants over a much longer period, expected to be 10 months.

Nevins also announced that “Californication,” which just had its most-watched season premiere ever, had been renewed for a fifth season. The season premieres of “Nurse Jackie” and “United States of Tara” are set for March 28, followed six days later by the debut of “The Borgias,” starring Jeremy Irons and exec produced by Neil Jordan.

Nevins noted that one of his immediate tasks succeeding Bob Greenblatt (whose move to NBC is expected to become official this month with the approval of the Comcast-NBC Universal deal) was to ensure that Showtime’s schedule has “no fallow periods,” with at least two or three originals airing each week of the year.

“It’s sort of a luxury to come in with shows that are working,” Nevins said. “That said, healthy networks that want to be on edge have to be in a constant state of renewal and reinvention.”

Nevins said that the baseball series, which will be co-produced by Major League Baseball Prods., began gestating last summer, before the Giants emerged as a major contender let alone title-winner. A combination of factors, from the dynamism of the players to their willingness to let Showtime go behind the scenes, led to San Francisco becoming a favorite, with their first Series title in more than half a century sealing the deal.

A preview episode will air in late March/early April near baseball’s Opening Day, with production continuing into the 2011 baseball season. Nevins envisions the series becoming a franchise featuring different teams each year.

Nevins also touted future shows for the channel, including Claire Danes starrer “Homeland, Don Cheadle starrer “House of Lies,” web-to-TV skein “Web Therapy” with Lisa Kudrow and “Gigolos,” an unscripted series about male escorts in Las Vegas.

“It’s not like we’re trying to appeal to a demo,” Nevins said of Showtime, whose subscriber base is approaching 19 million. “It’s about being deep and psychologically sophisticated and taking people places they don’t usually go.

“I think we’re getting to a good place where people hear of a new Showtime show and they give it the benefit of the doubt.”

Nevins added that he feels there’s a “lot of life” left in “Dexter” and gave a vote of confidence to “The Real L Word,” which is entering it’s second season this summer.

“I felt like there’s life in that idea,” Nevins said. “The network has had a long relationship with gay and lesbian audiences that I think is important to protect. I think there’s an interesting version of that show that we didn’t get to last year. I think we can make this show feel more Showtime, more premium. … Sometimes with those shows you get it right in year two.”

As has been noted, one project that Showtime won’t pursue is “The Kennedys,” the miniseries recently cut loose by History.

“I looked seriously at it,” said Nevins, who praised the program’s acting and production values. “What it came down to is it didn’t really feel Showtime; it didn’t really feel premium cable. I have great respect and love for (exec producer) Joel Surnow … but it didn’t really feel us.”

Nevins said he would never say never to a miniseries, but that he preferred to focus on ongoing skeins. “Series are renewable resources, and you give up that focus at your peril. We’re always going to look at longform, but not for foreseeable future is it going to be our bread and butter.”

Nevins said that the transition to a network exec role from his position as a producer at Imagine had gone easier than he expected, saying that with the freedom he in the job, he “can still feel largely like a producer.”