Jalen Williams, Chet Holmgren and Cason Wallace are out for the Thunder against the Grizzlies. That leaves more of Oklahoma City's offense with Shai Gilgeous-Alexander.
The Thunder have averaged 110.0 points through 8 games. Memphis has allowed 109.8 over the same span. Oklahoma City's reduced scoring options against that defense are the main reason for Under 225.5.
At the other end, the Thunder have allowed 108.8 points per game through 8 games.