Otzelberger announced Grill's move Tuesday. The 6-foot-3 guard started all 27 games for the Runnin' Rebels last season and averaged 9.1 points, 3.2 rebounds and 2.2 assists.
Grill signed with Iowa State out of high school in Maize, Kansas, and played for the Cyclones as a freshman in 2019-20, appearing in 29 of 32 games and making two starts.
Grill transferred after the season to UNLV, where Otzelberger was head coach. Grill initially had committed to play at South Dakota State when Oetzelberger was coach there. Otzelberger was hired at Iowa State four weeks ago.
"Caleb competes in everything that he does," Otzelberger said. "He takes pride in his defense, making the right play, shooting with accuracy and giving his all every time he takes the floor. His return to Ames will be very much anticipated and we're excited for what he will accomplish as a Cyclone."
Grill scored a career-high 27 points with seven 3-pointers against an Alabama team that went on to earn a No. 2 seed in the NCAA Tournament and advanced to the Sweet 16.
At Iowa State, Grill played 13.7 minutes per game as a freshman and averaged 2.1 points and 1.7 rebounds.