Maas Playing It by the Numbers : Baseball: Yankee rookie has stepped in for injured Don Mattingly and rewritten the record book.

Kevin Maas signed the last baseball, finishing off a boxful, and moved aside as Steve Sax took his place at a table in the New York Yankee clubhouse.

“Who’s he?” Sax said, tossing his head in Maas’ direction, where a baseball card representative had intercepted him. “Yeah,” Sax said, turning back to the baseballs, “Put the (guy) in the Hall of Fame.”

The razzing comes with the statistics. Kevin Maas, a 25-year-old rookie who has stepped in at first base for injured Don Mattingly, hit 10 home runs in his first 77 at-bats with the New York Yankees.

No one in major league history had reached 10 homers more quickly.

Maas hit a homer July 4 in his 15th at-bat, off the Kansas City Royals’ Bret Saberhagen.

He hit homers in three consecutive games, July 23-25, against the Texas Rangers.

He hit his 12th homer off the Seattle Mariners’ Erik Hanson, becoming the 21st player to hit a ball into the Kingdome’s upper deck, an estimated 448-foot shot.

After 100 at-bats, he had 12 homers, tying a major league record.

After 110, he had 13, another record.

“I’ve been in stretches like this before,” Maas said. “They don’t happen all the time, though. Not even once a year. It’s not a fluke, put it that way.”

As he prepared for one of the Yankees’ games against the Angels at Anaheim Stadium this week, Maas finished another piece of business and made his way to his stall, where a few reporters waited. Greg Cadaret, a Yankee pitcher whose stall was a few yards away, sniffed at the attention.

“What did you do? You haven’t even played yet.”

Maas laughed.

“That’s part of it,” he said. “You take it in stride. I can turn one cheek with the best of them.”

Maas, a Cal graduate with a degree in mechanical engineering, is adding a bit of suspense to a season that has been unsuspenseful for the Yankees, at least on the field.

A left-handed hitter, Maas has a swing that is built for Yankee Stadium, where the right-field foul pole is only 310 feet from home plate, and right field is 353 feet away.

Seven of his homers have come at Yankee Stadium, one in every 7.4 at-bats.

Even when Maas was playing at double-A Albany in 1988, people were thinking about it.

“I figured Yankee Stadium was the perfect place for him,” said Deron Johnson, the Angels’ batting instructor who was then coaching at Albany. “He has a nice, short swing and real strong hands. . . . He worked real hard. He knew where he wanted to go.”

Now, quickly it seems, he is there, and everyone wants a piece of him.

“It’s been pretty crazy,” Maas said. “That’s an understatement. . . . My days become very short. By the time I wake up to the time I go to bed, it seems like a couple of hours. I’m certainly trying to stay focused on baseball.”

After the series against the Angels, Maas is hitting .266 with 13 homers in 124 at-bats, with a slugging percentage of .605.

The question is whether this is the beginning of a long career or the start of one that will be buried in the Baseball Encyclopedia, along with his name.

For now, Maas has hit a homer every 9.5 at-bats.

Babe Ruth hit one every 11.8 at-bats over the course of his career; Ted Williams one every 14.8; Willie Mays one every 16.5; Hank Aaron one every 16.3; Carl Yastrzemski one every 26.5.

The 10-homer record was held by George Scott, who needed 79 at-bats with the Boston Red Sox in 1966 to do it.

The 13-homer record belonged to the Baltimore Orioles’ Sam Horn, who needed 123 at-bats to reach that mark in 1987.

Mass is tied for most homers in a first 100 at-bats with the Texas Rangers’ Dave Hostetler, who did it in 1982.

Some names and numbers flatter, some do not.

“You don’t build a career in a month and a half,” Maas said. “You build it by doing it every day.

“I’m really trying to play down what I’ve done. I still feel I have to prove myself every day.”