- Bats Right, Throws Right
- Height 5' 8", Weight 143 lb.
- High School Kofu Chugakkou
Naito ran track and played outfield in high school before dropping out. He was interested in being captain of a ship, not playing baseball, but one of his friends convinced him to try out for the Yomiuri Giants. Naito and his friend took a four-hour train trip to Tokyo and had one bat and a pair of sandals with him. He took two days of practice with the Giants and after getting home, "forgot all about it." Yomiuri sent him an acceptance letter and he panicked, as his family had not been notified and did not approve of him becoming a baseball player. With all the ships under American control at the time, Naito told his family that he would go to the Giants.
He was converted to catcher, where he had to make sure the team did not lose any baseballs during practice. He also became the gopher boy for Tetsuharu Kawakami, Shigeru Chiba and Noboru Aota as Japanese baseball at the time focused on the younger players helping the veterans. He went 1 for 2 with a triple for the club in 1949. The next year, Naito hit .214/.277/.274 in 113 games and stole 15 bases in 19 tries. Back into a reserve role, he went 3 for 24 in 25 games in 1951 and was 3 for 6 with five runs in 13 contests the next year. He played one game in the 1952 Japan Series, not getting to bat.
Yomiuri had spring training in Santa Maria, CA in 1953 and Naito had an offer to join the Brooklyn Dodgers after getting a few hits against them and making a nice play at second to retire Jim Gilliam, but Naito "knew that they were such big guys and so much powerful that I wouldn't be able to do it over there. So I said no." In 1953, the 22-year-old went 8 for 40 in 38 games and appeared in one game in the 1953 Japan Series, not batting. The 1954 season had him producing at a .234/.300/.328 clip in 78 AB over 52 games. Playing often in 1955, Naito hit .203/.253/.297 in 138 AB spread out over 104 games. In the 1955 Japan Series, he was 1 for 6 with a stolen base and a run scored. With Hawaiian players beginning to join the Giants, Naito used to introduce them to the local food at each new city they visited and Dick Kashiwaeda says that "we would have all been lost" without the support of Naito.
Hirofumi became the starting second baseman for the 1956 Giants. His .986 fielding percentage led all second basemen in the Central League. He hit .225/.248/.322 and then was 0 for 3 in the 1956 Japan Series. He remained the starter in 1957, putting up a .251/.306/.357 line with a career-high 28 walks, 17 doubles, 4 triples, 6 home runs and 48 RBI. He only went 2 for 19 with a steal in the 1957 Japan Series, the one Series in which he played regularly.
In 1958, Naito was back on the bench and batted .201/.270/.338 in 139 AB over 60 games. He was traded to the Kintetsu Buffaloes that off-season and became a regular again, hitting .250/.314/.327 in 248 AB in 67 games. As a starter in 1960, he had a .251/.304/.347 batting line. In 1961, he batted .240/.358/.310 in 100 AB over 70 games in his last year.
Overall, Naito had hit .232/.289/.323 in 2,112 AB over 886 games in Nippon Pro Baseball. After retiring, he began a restaurant in Kofu, Yamanashi, then was hired as a Kokutetsu Swallows coach in 1964. He later managed the Swallows ni-gun team in 1982 and worked as an overseer of Yomiuri's medical staff.