There used to be no limit to the number of clubs that a golfer could carry during a round. Many early golfers used relatively few clubs – think of those photographs of early golfers carrying their clubs in what we would nowadays call a pencil bag. When Francis Ouimet won the US Open in 1913 he carried only seven clubs. Or, more accurately, his 10-year old caddie Eddie Lowery did. Chick Evans also had only seven clubs in his bag when he won the US Open three years later.
Early golf clubs had wooden shafts, with hickory the most popular wood as it combined flexibility with durability. As they were made of a natural material, hickory-shafted clubs would not necessarily perform consistently through a set; indeed these clubs were often made as individual items rather than as part of a set.
Clubmakers begun experimenting with metal-shafted clubs as early as the late 19th century and in 1924 Herbert C Lagerblade became the first player to use steel-shafted golf clubs at a US Open. Metal shafts offered greater consistency between clubs in the same set and offered more carry on shots. Many players were reluctant to move away from the hickory-shafted clubs they were familiar with; others were keen to explore the advantages that steel-shafted ones provided. Some compromised by carrying both hickory- and steel-shafted clubs in their bags.
During the 1920s and 1930s the number of clubs players were carrying ballooned. When Lawson Little won the Amateur Championship in 1934 he had 31 clubs in his bag. At the 1935 US Open the average number of clubs the players were carrying was 18. One entrant had 32, as he carried a set of right-handed clubs and another set of left-handed clubs. There are tales of caddies having to carry two bags round the course to get all the clubs in. Things had got ridiculous.
Golfing authorities were also concerned that the sheer number of clubs players were carrying reduced the need for skill in executing shots; also that the less affluent golfer was being penalised as they could not afford a huge variety of clubs.
So the United States Golf Association decreed that no more than 14 clubs could be carried during a round as from January 1, 1938. The R&A wrote this rule into the 13th edition of the Rules of Golf which came into effect on January 1, 1939.
As to why 14 was selected as the magic number, no-one is sure. This number seems to have been proposed at the meeting of the USGA and accepted without much debate.
A story regularly trotted out is that 14 arose from a discussion between Bobby Jones and Tony Torrance at the 1936 Walker Cup where one of the US players, Scotty Campbell, was carrying 32 clubs. Jones remarked that he had 16 clubs when he won the Grand Slam in 1930; Torrance, captain of the Great Britain & Ireland Walker Cup side in 1932, carried 12 clubs. Thus 14 came about as an average of these two figures.