Complex sentence: The league set deadlines for changes in the rosters, which were allowed only during the first half of the season, and the number of games played has historically varied from 40 to 80 games per season.
Split into simpler sentences: The league set deadlines for changes in the rosters, which were allowed only during the first half of the season. The number of games played has historically varied from 40 to 80 games per season.