The Steel Ball Run was a transcontinental horse race serving as the main setting of JoJo's Bizarre Adventure: Part 7. However, we never received an explicit answer as to why it was named in the way it was in-universe, nor out-of-universe. The only other article we can reasonably assume this name is referencing is the steel ball, used by the Zeppeli family. But, if anything, this complicates things further, since the Zeppelis should have no relevant connection to the race's organiser, Steven Steel. So why was it named the Steel Ball Run?
This race is quite literally a reference to the movie Cannonball Run, where teams gathered in Connecticut to start a cross-country car race. What is a cannonball? Typically a steel ball.