Complex sentence: Board track, or motordrome, racing was a type of motorsport, popular in the United States between the second and third decades of the 20th century, where competition was conducted on oval race courses with surfaces composed of wooden planks.
Split into simpler sentences: Board track, or motordrome, racing was a type of motorsport popular in the United States between the second and third decades of the 20th century. Competition was conducted on oval race courses with surfaces composed of wooden planks.