Complex sentence: In his first season, Mendenhall led his team to a 6-5 regular season record when a weak defensive secondary cost the cougars several close games including a 51-50 loss to nationally ranked TCU.
Split into simpler sentences: In his first season, Mendenhall led his team to a 6-5 regular season record. Mendenall's defensive secondary was weak, a significant problem for the Cougars in several close games including a 51-50 loss to nationally ranked TCU.