[1] He was a two-time winner of the Eiji Sawamura Award (2003, 2006), but did not pitch in a regular season game after October 2007 due to various shoulder injuries.

While Saito made his first appearance at the ichigun (Japanese equivalent of "major league") level in 1997, just his second year in the pros, his development was often hindered by his proneness to injury.

In particular, Saito was plagued by a chronically loose shoulder joint, a condition so troubling for pitchers that coaches even suggested switching positions and becoming a hitter (as evidence of this, he was once called upon to pinch-hit in a nigun ("minor league" or "farm team") game, playing left field in the next inning).

After undergoing surgery on his right shoulder and missing the entire 1998 season due to rehab, Saito finally posted his first win with the ichigun in 2000.

He went on to win five games that season, four of which were after the All-Star break in the thick of the pennant race, but was not called upon to start in the Japan Series when the Hawks eventually won the league title.

[3] That year, then-Hanshin Tigers ace Kei Igawa had also posted 20 wins, making it the first time since 1982 that both Japanese leagues had produced 20-game winners.

In 2005, despite being named the Hawks' Opening Day starter during Spring training, recurring pains in his shoulder forced Saito to commit to rehab again (Tsuyoshi Wada started in his place).

[6] Nevertheless, he made his first start of the season on April 27 against the Hokkaido Nippon Ham Fighters, the first of a 15-game win streak that lasted until　September 7 in a game against the Orix BlueWave.

Saito asked to have his name dropped from the selection process for the Japanese national team that would play in the inaugural World Baseball Classic during 2006 Spring training, instead focusing on adjusting his mechanics so that they would conform to the new rules the NPB had decided to employ regarding pitching motions.

While he gave up just two runs in 162⁄3 combined innings, the Hawks were shut out 1–0 in both games, the former by Daisuke Matsuzaka,[10] the latter by Fighters left-hander Tomoya Yagi.

After the Fighters scored the game-winning run off him in the ninth inning of the latter game, Saito could no longer contain his frustration, falling to the ground in tears as teammates Julio Zuleta and Jolbert Cabrera helped him off the mound.

It was his tenth attempt at his first win in the playoffs (excluding the Japan Series), but he could not shut down the Marines offense and the Hawks went on to lose in the first stage yet again.

Saito traveled to the United States in January prior to the 2008 season to have endoscopic rotator cuff surgery on his right shoulder,[12] which had worsened over time due to accumulate fatigue.

Saito spent much of January 2009 in Arizona as part of his rehab effort, hoping to be ready in time for the upcoming regular season, but his shoulder recovery did not progress as planned.