The Yankees had pinstripes before they had Babe Ruth. It's an urban myth that they designed the pinstripes so that the Babe wouldn't look fat.
Some caps also contain the pinstriped design.
New York Yankees
What would become the most recognizable insignia in sports the interlocking "NY" made its first appearance on the uniforms of the New York Highlanders in 1909. The design was actually created in 1877 by Louis B. Tiffany for a medal to be given by the New York City Police Department to Officer John McDowell, the first NYC policeman shot in the line of duty. Perhaps because one of the club's owners, Bill Devery, was a former NYC police chief, the design was adopted by the Highlanders. It first appeared on both the cap and on the jersey's left sleeve, replacing the separated "N" and "Y" which had appeared on the left and right breast each season since 1903 with the exception of 1905. For that season only, the "N" and "Y" were merged side by side into a monogram on the left breast actually a forerunner of the now legendary emblem.
In 1912, their final season at Hilltop Park, the Yankees as they were now commonly known made a fashionable debut at their home opener on April 11. Their traditional white uniforms were now trimmed with black pinstripes, creating a look that would become the most famous uniform design in sports history. The Yankees, however, were not the first team with pinstripes and would actually abandon the look for the next two seasons. By 1915, though, the pinstripes were back for good and, with the exception of the cap, the uniform would remain relatively unchanged.
(Oxford English Dictionary)
A person who wears pinstriped clothing; spec. (a) a player in the New York Yankees baseball team; (b) a businessman or businesswoman, esp. one belonging a prominent corporate company. Cf. PINSTRIPE n. 3.
1959 Los Angeles Times 13 Apr. IV. 7 (headline) Future Pin-Stripers. Quartet of Rookies Fighting for Place on Yankee Roster.
1979 Washington Post 17 Apr. B1/3 A reminder that not all lawyers are corporate pin-stripers, that some of them choose to challenge the system rather than serve it.
30 June 1949, Walla Walla (WA) Union-Bulletin, pg. 17:
Not only did the pin-stripers get a lot of publicity out of the bad heel, but an insufferable amount from Joe's (DiMaggio -- ed.) point of view, but since he has returned to the lineup, they will not only get the publicity, but customers will come a running to see how many more home runs he is going to hit.
7 April 1959, Daily Review (Hayward, CA), pg. 10:
There was a rosier day eight years ago when Ed, then the pride of Jefferson High School in nearby Daly City, signed up with the bronx pinstripers for that nice bonus.
13 April 1959, Los Angeles Times, pg. C7:
Quartet of Rookies Fighting
for Place on Yankee Roster
1 December 1966, Washington (DC) Post, pg. C2:
Mike Burke, new boss of the New York Yankees who came over from the Columbia Broadcasting System, has given the oder to "humanize" the pinstripers.
19 January 1977, Washington (DC) Post, pg. D9:
The New York Yankees, who, with renovated stadium and pennant winner topped 2 million in attendance last year for the first time since 1950, report a 65 per cent rise in season-ticket sales vis-a-vis this point in winter '76; they attribute much of the gain to interest in pinstripers-to-be Reggie Jackson and Don Gullet.