Spring training workouts in February had just begun, the Twins were getting their first glimpses of new infielder Tsuyoshi Nishioka, and bench coach Scott Ullger was asked for his early impressions.

Ullger liked what he saw but also added, "We want him to make sure he clears the bag at second so he doesn't get killed."

Nishioka worked on that and stayed out of harm's way throughout camp. He made it through 5 2/3 games in the regular season before trouble found him, and now he's out four to six weeks, and maybe longer, because of a broken left fibula, an estimate made after an exam by Dr. John Steubs at Target Field on Friday.

Nishioka tried to clear the bag in the seventh inning Thursday as the Yankees' Nick Swisher closed in. Nishioka was a little off the bag but still in range of Swisher, who executed what most believe was a clean take-out slide. Nishioka was upended and his leg was broken.

No surgery or cast is needed, and Twins manager Ron Gardenhire said Nishioka could return in four to six weeks. Nishioka hopes to start running in about two weeks, after swelling and soreness are expected to subside.

"It was a fracture, but it wasn't a huge injury that will be something that would mean the season," Nishioka said. "So I just want to get back as soon as possible on the field."

Baserunners have been going after middle infielders for years. The Twins' Michael Cuddyer slides in as hard as anyone in the league to try to snuff out double plays.

Did Nishioka have time to clear the bag more? To jump in the air? To step backward?

The biggest question: Is he used to the contact?

If Thursday's game was played in Japan, Nishioka might not have needed a crutch to walk out to the first base line for Opening Day introductions on Friday.

KSTP's Dan Gladden, who won World Series in 1987 and 1991 with the Twins and a Japan Series title with the Yomiuri Giants in 1994, said during Thursday's broadcast that the only time he saw aggressive baserunning like Swisher's in the Japanese Leagues was when American players did it.

"When I got over there I told them, 'I don't slide to the bag. We are taught to break up double plays,' " Gladden said between innings on Friday. "The coach told me, 'We expect the Americans to play that way.' "

Wally Yonamine, who died in February at age 85, was the Hawaiian-born son of Japanese parents -- and the first American-born player in the Japanese leagues following World War II. Anti-American sentiment was running high then. Yonamine didn't help matters with his aggressive play, which included take-out slides at second base.

"He introduced 'aggressive' baserunning to baseball in Japan in the '50s," Seigo Masubuchi, Tokyo native and director of international development for the St. Paul Saints, wrote in an e-mail.

While Yonamine introduced that style, it appears that it never caught on. Gladden said that most collisions at home plate were avoided in Japan when he played there, and Masubuchi said Swisher's slide would be frowned upon today.

"No, not that 'hard level,' " Masubuchi wrote. "Runners tried to break double plays [in Japan], but they don't do in ways [to] possibly hurt other players like Swisher did.

"I'm sure Nishioka knew he would encounter hard slides like Swisher did, and he must have practiced for it during spring training, but split-second moment like that it must be tough to jump or do whatever to avoid getting hit by aggressive baserunning."

Nishioka, by the way, is listed at 176 pounds in the Twins media guide. The Yankees guide has Swisher at 210.

Nishioka, using that crutch, made his way out for pregame introductions Friday and received a loud ovation from the announced crowd of 40,714.

It was his first introduction at Target Field -- a day after his latest introduction to the way major league baseball is played.

"I wanted to show the fans not the impression of Nishioka on crutches," he said through a translator, "but Nishioka with the bat."

La Velle E. Neal III• lneal@startribune.com