Television ratings for National Basketball Association games are down 15% so far this season, a drop that the league and its TV partners attribute to injuries that are keeping some of the NBA’s biggest stars on the sidelines.

NBA games on national TV drew an average of 885,000 viewers in the U.S. in the first eight weeks of the season, according to Nielsen, compared with about one million over the same period last year and 1.2 million two years ago.

Some...