Surprise, Ariz. ? The Kansas City Royals optioned shortstop Angel Berroa, the 2003 American League Rookie of the year, to Triple-A Omaha on Saturday.

The demotion came one day after the Royals acquired Tony Pena Jr. in a trade with the Atlanta Braves. Manager Buddy Bell said Pena would be his starting shortstop.

Berroa, 29, has struggled since his rookie season and showed little sign of improvement in spring training this year.

“It’s not something he was happy about, obviously,” Bell said. “Angel is going to be a good player again. He’s a good kid and works hard. He had all the ingredients to get better. He knows what he needs to do.”

It is a costly cut for the Royals, who signed Berroa to a multiyear contract after his rookie season. They still owe him $8 million for the 2007-08 seasons, plus a $500,000 buyout for 2009 if they do not pick up the option year of his contract.

Berroa edged out Hideki Matsui by four votes in the 2003 AL Rookie of the Year balloting. It was the closest vote in either league since 1979.

Berroa hit .287 and led AL rookies with 92 runs and ranked third with 163 hits and 21 stolen bases. His 17 home runs, and his 73 RBIs were the most by a rookie shortstop since Nomar Garciaparra hit 30 homers with 98 RBIs in 1997 with the Boston Red Sox.

Berroa, however, never came close to approaching his rookie offense again. He hit only .234 last season with 28 extra-base hits. The past two years, he has had more errors than walks – 18 errors and 14 walks in 2006 and 25 errors and 18 walks in 2005.

The Royals also reassigned outfielder Billy Butler, a 2004 first-round pick, to the minor leagues, although he hit .419 with five doubles and 10 RBIs in 19 spring games. While Butler’s bat is nearly ready for the majors, Bell said the club wants him to improve his defense.