Complex sentence: It chose men's soccer because three of the confirmed members for 2013--14 (CSU Bakersfield, Grand Canyon, and Seattle) already sponsored the sport, filling out its soccer ranks by attracting four schools from the Mountain Pacific Sports Federation.
Split into simpler sentences: It chose men's soccer because three of the confirmed members for 2013--14 (CSU Bakersfield, Grand Canyon, and Seattle) already sponsored the sport. It filled out its soccer ranks by attracting four schools from the Mountain Pacific Sports Federation.