He was an assistant coach for the Washington State Cougars baseball team from 2016 to 2019.

[1] The 6 ft (1.8 m), 210 lb (95 kg) Horner had a nine-year playing career, all within the Mariners' minor leagues, as a catcher from 1996 to 2004.

The highest level of the minors Horner reached was Triple-A in 2000 with the Tacoma Rainiers.

Horner led the 2009 Mavericks to an 83–57 (.593) record, winning the first- and second-half California League South Division titles.

[4] On July 30, 2010, he resigned as High Desert's manager to become assistant baseball coach of Texas Tech University, serving through the 2012 campaign.