This is the 10719th most frequent German word.
rodelsport
Rodelsport: The sport of tobogganing or sledding.
The word 'rodelsport' here is used as the subject of the sentence, referring to the sport of sledding collectively.
Der Rodelsport ist im Winter sehr beliebt.
Luge sport is very popular in winter.
In this sentence, 'rodelsport' is the direct object, referring again to engaging in the activity of sledding.
Viele Menschen lernen Rodelsport in den Alpen.
Many people learn luge sport in the Alps.
Here, 'rodelsport' is part of a compound noun, signifying a competitive context for the activity.