Early rugby and football players wore light jerseys and pants without pads while running around the field, trying to avoid being tackled, which legally occurred only by defenders grabbing the ball carrier between the shoulders and the waist. Grabbing runners by the torso resulted in the frequent tearing of runners' jerseys, so Ledru P. Smock of Princeton had his tailor make a tight-fitting, long-sleeved canvas jacket that was difficult to grasp or tear. His teammates initially laughed at his outfit until they tried tackling him, after which they converted to wearing similar jackets, tightly laced in front. 

The long sleeves on Smock's original jacket restricted arm movements, so the Princetonians switched to wearing canvas vests, which they wore for the first time against Harvard in April 1877. Under the vests, Princeton wore shirts with black sleeves and orange stripes, earning them the first college sports nickname, the Tigers. Soon afterward, sporting goods manufacturers offered the sleeved and vest styles that, along with quilted pants, became the standard football outfit until the turn of the century.

A shortcoming of the separate vests and football pants was that tacklers could grab the top of the ball carrier's pants or his belt to assist in the tackle. (Since this was the same period during which some runners sewed handles on their pants so their teammates could assist in pulling them forward through piles, the 'top-of-the-pants-as-handle' functionality worked both ways.)

Recognizing the pants grabbing problem, the smarty pants at Harvard connected the bottom of their vests to the top of their trousers. A report on the 1898 Harvard-Carlisle game mentioned that Harvard warmed up in standard gear but changed during pre-game to outfits that "had their jackets fastened to their breeches to be less easily tackled, and to do away with the belt." Unfortunately, additional details regarding Harvard's gear are not available. Still, Harvard likely contributed to Spalding's development of the 'Varsity Union Suit, which they tested in 1901 and released to the market in 1902.

Spalding's football union suit was a single garment, like the type of underwear that came on the market shortly after the Civil War. It had a moleskin or canvas vest, football pants with cane-reinforced thigh pads and quilted padding elsewhere, set off by an elastic band connecting the two and covering an internal belt. As before, colored stockings and jerseys worn under the union suits distinguished one team from another.

Perhaps one-third of players and teams wore union suits in games during the century's first decade. Period images show games in which everyone on the field wears football sweaters along with their pants, others in which both teams sport union suits, and still others in which players wear a mixture. As was often the case before the 1920s, team uniforms were not uniform.

Union suits largely disappeared from use by the mid-1910s. Their demise stemmed from several changes. One was the move away from shoulder pads sewn on the exterior of jerseys to those worn under the jersey. The under-the-jersey shoulder pads of the 1910s offered better protection than the exterior pads and did not fit under the tight-fitting union suit vests. 

The period also witnessed players starting to wear numbers on their backs. While early numbers often were painted on canvas patches sewn onto the jerseys, they soon transitioned to embroidered numbers that were more difficult to sew on the union suit canvas or did not display well once in place. Union suits also bucked the general equipment trend toward separates as sporting goods manufacturers increasingly produced modular equipment. For example, they stopped integrating quilted and caned pads into pants and instead created pants with interior pockets allowing players to insert the thigh and knee pads of their choice – or not. 

Likewise, the move toward a more open game placed a premium on speed, leading players to reduce equipment and its weight whenever possible. Vests worn atop jerseys, especially water-absorbing canvas vests, no longer made sense and were cast aside. Finally, union suits were also not the most eye-pleasing piece of equipment to appear on the gridiron, and did not help distinguish one team from the next in the large stadiums where teams set football fashion trends. Players wearing exposed, full jerseys helped visually separate one team from the next.

With the elimination of union suits, football players took on their modern silhouettes. While it would be understandable for someone seeing the image of a union suit-clad player to not recognize them as being a football player, players of the late 1910s and beyond are instantly understood to be wearing gridiron gear. Of course, many other changes in football gear were to come, and some, like the union suit, are no longer with us, but each played a part in the evolution of the game that brought us to our current state.

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