It used to be that a tennis player while serving the ball could be moving––walking or running toward the service line.
Furthermore he or she could use this running start to advance quickly to the net as part of the service motion.
That all changed beginning in 1903.
The newly proposed rule stated “It is not a fault if one only of the server’s feet do not touch the ground at the moment at which the service is delivered. He shall place both feet on the ground immediately before serving, and not take a running or a walking start.” (New York Times, June 7, 1903).
This rule was arbitrated by the English who did not care for this practice employed by American players who often appeared to arrive at the net before the ball did.
The Brits got this rule in place to quell the U.S. enthusiasm for rushing the net.
So, from 1908 until 1960, a tennis player had to keep one foot on the ground at all times during the service motion. If both feet left the ground it was ruled a foot fault.
The rule was amended in 1961.
Image what the serve would look like today if players had one foot nailed to the ground?