TEMPE, Ariz. -- Arizona State softball coach Craig Nicholson has resigned just before the start of his third season in the desert, citing personal medical reasons.

Sun Devils athletic director Ray Anderson made the announcement in a statement Monday but did not provide details.

Assistant coaches Robert Wagner and Letty Olivarez will serve as co-interim coaches this season, which starts Feb. 11 after five fall games.

Nicholson was hired in 2014 from Ball State to replace Clint Myers, who led the Sun Devils to a pair of national titles. He went 82-34-1 and led the 2014 and 2015 teams to the NCAA Tournament. He is 1,046-286-1 in 20 seasons as a head coach.